diff --git a/app/src/components/settings/panels/AIPanel.tsx b/app/src/components/settings/panels/AIPanel.tsx
index c89438030..3745e4a41 100644
--- a/app/src/components/settings/panels/AIPanel.tsx
+++ b/app/src/components/settings/panels/AIPanel.tsx
@@ -45,8 +45,10 @@ import {
   openhumanHeartbeatSettingsSet,
   openhumanHeartbeatTickNow,
 } from '../../../utils/tauriCommands/heartbeat';
+import { ConfirmationModal } from '../../intelligence/ConfirmationModal';
 import SettingsHeader from '../components/SettingsHeader';
 import { useSettingsNavigation } from '../hooks/useSettingsNavigation';
+import { useReembedBackfillModal } from './useReembedBackfillModal';
 
 // ─────────────────────────────────────────────────────────────────────────────
 // Types
@@ -335,7 +337,9 @@ function useAISettings() {
     [saved]
   );
 
-  const save = useCallback(async () => {
+  // Returns true only when persistence actually succeeded, so callers
+  // (e.g. the #1574 re-embed-status check) don't act on a failed save.
+  const save = useCallback(async (): Promise<boolean> => {
     try {
       // Defensive verification at global-Save time. Each provider that is new
       // or whose endpoint changed since the last saved snapshot is re-probed
@@ -358,14 +362,16 @@ function useAISettings() {
         } catch (probeErr) {
           const msg = probeErr instanceof Error ? probeErr.message : String(probeErr);
           setError(`Could not reach ${p.label}: ${msg}. Settings were not saved.`);
-          return;
+          return false;
         }
       }
 
       await persist(draft);
+      return true;
     } catch (err) {
       const message = err instanceof Error ? err.message : 'Failed to save AI settings';
       setError(message);
+      return false;
     }
   }, [saved, draft, persist]);
 
@@ -1974,6 +1980,9 @@ const AIPanel = ({ embedded = false }: AIPanelProps = {}) => {
   const { navigateBack, breadcrumbs } = useSettingsNavigation();
   const { saved, draft, setDraft, isDirty, save, persist, discard, loading, error, reload } =
     useAISettings();
+  // #1574 §4b: advisory re-embed modal, driven by the backend status RPC.
+  // Logic lives in a unit-testable hook (see useReembedBackfillModal).
+  const { reembed, handleSave, dismissReembed } = useReembedBackfillModal(save);
   const ollama = useOllamaStatus();
   const installed = useInstalledModels(ollama.snapshot);
   const [editing, setEditing] = useState<CloudProvider | 'new' | null>(null);
@@ -2220,11 +2229,27 @@ const AIPanel = ({ embedded = false }: AIPanelProps = {}) => {
         <SaveBar
           diffSummary={diffSummary}
           changeCount={diffSummary.length}
-          onSave={() => void save()}
+          onSave={() => void handleSave()}
           onDiscard={discard}
         />
       )}
 
+      <ConfirmationModal
+        modal={{
+          isOpen: reembed.open,
+          title: 'Re-indexing memory',
+          message:
+            `Embeddings are being reprocessed. ${reembed.pending} memory item(s) ` +
+            `are being re-embedded under the current model — semantic recall is ` +
+            `reduced until this finishes. Keyword search keeps working, and ` +
+            `re-embedding continues in the background if you close this.`,
+          confirmText: 'OK',
+          onConfirm: dismissReembed,
+          onCancel: dismissReembed,
+        }}
+        onClose={dismissReembed}
+      />
+
       {editing && (
         <CloudProviderEditor
           initial={editing === 'new' ? null : editing}
diff --git a/app/src/components/settings/panels/useReembedBackfillModal.test.tsx b/app/src/components/settings/panels/useReembedBackfillModal.test.tsx
new file mode 100644
index 000000000..885985fbe
--- /dev/null
+++ b/app/src/components/settings/panels/useReembedBackfillModal.test.tsx
@@ -0,0 +1,111 @@
+import { act, renderHook } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { memoryTreeBackfillStatus } from '../../../utils/tauriCommands/memoryTree';
+import { useReembedBackfillModal } from './useReembedBackfillModal';
+
+vi.mock('../../../utils/tauriCommands/memoryTree', () => ({ memoryTreeBackfillStatus: vi.fn() }));
+
+const status = vi.mocked(memoryTreeBackfillStatus);
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+describe('useReembedBackfillModal (#1574 §4b)', () => {
+  it('does not check status or open the modal when save fails', async () => {
+    const save = vi.fn().mockResolvedValue(false);
+    const { result } = renderHook(() => useReembedBackfillModal(save));
+
+    await act(async () => {
+      await result.current.handleSave();
+    });
+
+    expect(save).toHaveBeenCalledTimes(1);
+    expect(status).not.toHaveBeenCalled();
+    expect(result.current.reembed).toEqual({ open: false, pending: 0 });
+  });
+
+  it('opens the modal when save succeeds and a backfill is in progress', async () => {
+    const save = vi.fn().mockResolvedValue(true);
+    status.mockResolvedValue({ in_progress: true, pending_jobs: 7 });
+    const { result } = renderHook(() => useReembedBackfillModal(save));
+
+    await act(async () => {
+      await result.current.handleSave();
+    });
+
+    expect(result.current.reembed).toEqual({ open: true, pending: 7 });
+  });
+
+  it('stays closed when save succeeds but no backfill is in progress', async () => {
+    const save = vi.fn().mockResolvedValue(true);
+    status.mockResolvedValue({ in_progress: false, pending_jobs: 0 });
+    const { result } = renderHook(() => useReembedBackfillModal(save));
+
+    await act(async () => {
+      await result.current.handleSave();
+    });
+
+    expect(result.current.reembed.open).toBe(false);
+  });
+
+  it('swallows a status-check error and stays closed', async () => {
+    const save = vi.fn().mockResolvedValue(true);
+    status.mockRejectedValue(new Error('rpc down'));
+    const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    const { result } = renderHook(() => useReembedBackfillModal(save));
+
+    await act(async () => {
+      await result.current.handleSave();
+    });
+
+    expect(result.current.reembed.open).toBe(false);
+    expect(warn).toHaveBeenCalled();
+    warn.mockRestore();
+  });
+
+  it('polls while open: updates pending, then auto-closes when the backfill drains', async () => {
+    vi.useFakeTimers();
+    const save = vi.fn().mockResolvedValue(true);
+    status
+      .mockResolvedValueOnce({ in_progress: true, pending_jobs: 9 }) // handleSave open
+      .mockResolvedValueOnce({ in_progress: true, pending_jobs: 4 }) // poll #1
+      .mockResolvedValueOnce({ in_progress: false, pending_jobs: 0 }); // poll #2 → close
+    const { result } = renderHook(() => useReembedBackfillModal(save));
+
+    await act(async () => {
+      await result.current.handleSave();
+    });
+    expect(result.current.reembed).toEqual({ open: true, pending: 9 });
+
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(2000);
+    });
+    expect(result.current.reembed.pending).toBe(4);
+
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(2000);
+    });
+    expect(result.current.reembed.open).toBe(false);
+  });
+
+  it('dismissReembed closes the modal (background backfill unaffected)', async () => {
+    const save = vi.fn().mockResolvedValue(true);
+    status.mockResolvedValue({ in_progress: true, pending_jobs: 2 });
+    const { result } = renderHook(() => useReembedBackfillModal(save));
+
+    await act(async () => {
+      await result.current.handleSave();
+    });
+    expect(result.current.reembed.open).toBe(true);
+
+    act(() => {
+      result.current.dismissReembed();
+    });
+    expect(result.current.reembed).toEqual({ open: false, pending: 0 });
+  });
+});
diff --git a/app/src/components/settings/panels/useReembedBackfillModal.ts b/app/src/components/settings/panels/useReembedBackfillModal.ts
new file mode 100644
index 000000000..ec5561b9c
--- /dev/null
+++ b/app/src/components/settings/panels/useReembedBackfillModal.ts
@@ -0,0 +1,84 @@
+/**
+ * #1574 §4b: advisory re-embed-backfill modal state, driven entirely by the
+ * backend status RPC.
+ *
+ * After a settings save, the core's coverage-gated `ensure_reembed_backfill`
+ * has already decided whether the embedder change needs a re-embed; this hook
+ * just surfaces its progress (no fragile frontend "did the embedder change"
+ * detection). Extracted from `AIPanel` so the logic is unit-testable in
+ * isolation rather than only via a full 2000-line component render.
+ */
+import { useCallback, useEffect, useState } from 'react';
+
+import { memoryTreeBackfillStatus } from '../../../utils/tauriCommands/memoryTree';
+
+export interface ReembedState {
+  open: boolean;
+  pending: number;
+}
+
+export interface ReembedBackfillModal {
+  reembed: ReembedState;
+  /** Wrap a settings-save: persist, then (only on success) surface re-embed progress. */
+  handleSave: () => Promise<void>;
+  /** Close the advisory modal (re-embed continues in the background). */
+  dismissReembed: () => void;
+}
+
+const POLL_MS = 2000;
+
+/**
+ * @param save Persists settings; resolves `true` only on a successful write
+ *   (a failed save did not change the embedder, so nothing to surface).
+ */
+export function useReembedBackfillModal(save: () => Promise<boolean>): ReembedBackfillModal {
+  const [reembed, setReembed] = useState<ReembedState>({ open: false, pending: 0 });
+
+  const handleSave = useCallback(async () => {
+    const ok = await save();
+    if (!ok) return;
+    try {
+      const st = await memoryTreeBackfillStatus();
+      if (st.in_progress) {
+        setReembed({ open: true, pending: st.pending_jobs });
+      }
+    } catch (e) {
+      console.warn('[ai-panel] backfill status check failed', e);
+    }
+  }, [save]);
+
+  const dismissReembed = useCallback(() => setReembed({ open: false, pending: 0 }), []);
+
+  useEffect(() => {
+    if (!reembed.open) return;
+    let cancelled = false;
+    // Serialize polls — if a status call takes >POLL_MS, skip the next tick
+    // rather than overlapping requests.
+    let inFlight = false;
+    const id = window.setInterval(() => {
+      if (inFlight) return;
+      inFlight = true;
+      void (async () => {
+        try {
+          const st = await memoryTreeBackfillStatus();
+          if (cancelled) return;
+          if (!st.in_progress) {
+            setReembed({ open: false, pending: 0 });
+          } else {
+            setReembed(r => ({ ...r, pending: st.pending_jobs }));
+          }
+        } catch (e) {
+          console.warn('[ai-panel] backfill poll failed', e);
+        } finally {
+          inFlight = false;
+        }
+      })();
+    }, POLL_MS);
+    return () => {
+      cancelled = true;
+      window.clearInterval(id);
+    };
+  }, [reembed.open]);
+
+  return { reembed, handleSave, dismissReembed };
+}
diff --git a/app/src/utils/tauriCommands/memoryTree.test.ts b/app/src/utils/tauriCommands/memoryTree.test.ts
index 8ac1df81f..68a5cfd2c 100644
--- a/app/src/utils/tauriCommands/memoryTree.test.ts
+++ b/app/src/utils/tauriCommands/memoryTree.test.ts
@@ -8,6 +8,7 @@ import { beforeEach, describe, expect, type Mock, test, vi } from 'vitest';
 
 import { callCoreRpc } from '../../services/coreRpcClient';
 import {
+  memoryTreeBackfillStatus,
   memoryTreeChunkScore,
   memoryTreeDeleteChunk,
   memoryTreeEntityIndexFor,
@@ -355,3 +356,27 @@ describe('memoryTreeGraphExport', () => {
     expect(out.edges).toHaveLength(1);
   });
 });
+
+describe('memoryTreeBackfillStatus', () => {
+  test('dispatches openhuman.memory_tree_memory_backfill_status and unwraps', async () => {
+    mockCallCoreRpc.mockResolvedValueOnce({
+      result: { in_progress: true, pending_jobs: 3 },
+      logs: ['memory_tree: backfill_status in_progress=true pending=3'],
+    });
+
+    const out = await memoryTreeBackfillStatus();
+
+    expect(mockCallCoreRpc).toHaveBeenCalledWith({
+      method: 'openhuman.memory_tree_memory_backfill_status',
+    });
+    expect(out.in_progress).toBe(true);
+    expect(out.pending_jobs).toBe(3);
+  });
+
+  test('handles bare-value responses (no logs envelope)', async () => {
+    mockCallCoreRpc.mockResolvedValueOnce({ in_progress: false, pending_jobs: 0 });
+    const out = await memoryTreeBackfillStatus();
+    expect(out.in_progress).toBe(false);
+    expect(out.pending_jobs).toBe(0);
+  });
+});
diff --git a/app/src/utils/tauriCommands/memoryTree.ts b/app/src/utils/tauriCommands/memoryTree.ts
index f01e4ff26..adc83a400 100644
--- a/app/src/utils/tauriCommands/memoryTree.ts
+++ b/app/src/utils/tauriCommands/memoryTree.ts
@@ -603,3 +603,31 @@ export async function memoryTreeGraphExport(
   );
   return out;
 }
+
+/**
+ * #1574 §4b: per-model embedding re-embed backfill status. The AI settings
+ * panel polls this after an embedder change to warn that semantic recall
+ * is reduced until the new embedding space is fully re-embedded, and to
+ * dismiss the warning once the chain drains. Backed by
+ * `openhuman.memory_tree_memory_backfill_status`.
+ */
+export interface BackfillStatus {
+  /** True while a re-embed backfill still has work pending. */
+  in_progress: boolean;
+  /** Count of `reembed_backfill` jobs in ready/running state. */
+  pending_jobs: number;
+}
+
+export async function memoryTreeBackfillStatus(): Promise<BackfillStatus> {
+  console.debug('[memory-tree-rpc] memoryTreeBackfillStatus: entry');
+  const resp = await callCoreRpc<BackfillStatus | ResultEnvelope<BackfillStatus>>({
+    method: 'openhuman.memory_tree_memory_backfill_status',
+  });
+  const out = unwrapResult(resp);
+  console.debug(
+    '[memory-tree-rpc] memoryTreeBackfillStatus: exit in_progress=%s pending=%d',
+    out.in_progress,
+    out.pending_jobs
+  );
+  return out;
+}
diff --git a/src/openhuman/composio/action_tool.rs b/src/openhuman/composio/action_tool.rs
index cdab7fbb7..ffa22fb7e 100644
--- a/src/openhuman/composio/action_tool.rs
+++ b/src/openhuman/composio/action_tool.rs
@@ -386,45 +386,31 @@ mod tests {
     // construction time, so a mid-session `composio.mode` toggle is
     // honoured on the very next per-action execute.
 
-    #[tokio::test]
-    async fn factory_routes_through_backend_when_mode_is_backend() {
-        // Default `Config` has `composio.mode = "backend"`. Without a
-        // stored backend session token the factory returns
-        // `Err("no backend session ...")`. Assert that the error text
-        // points at the backend code path (not direct-mode or staging-
-        // api), confirming the routing branch.
-        //
-        // Production `.execute(..)` calls `load_config_with_timeout()`
-        // per call which reads from `~/.openhuman/config.toml` (or the
-        // workspace pointed at by `OPENHUMAN_WORKSPACE`). To isolate
-        // the test from the dev's real config we hold `TEST_ENV_LOCK`,
-        // point `OPENHUMAN_WORKSPACE` at a tempdir, and persist the
-        // test's `Config` to that tempdir's `config.toml` before
-        // invoking the tool.
-        use crate::openhuman::config::TEST_ENV_LOCK;
-        let _env_guard = TEST_ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
-
+    // These two tests assert the *factory routing decision* by mode. They
+    // call `create_composio_client(&Config)` directly — the pure routing
+    // function — instead of going through `tool.execute()`, which reloads
+    // config via `load_config_with_timeout()` (reads `OPENHUMAN_WORKSPACE`)
+    // and was therefore subject to a parallel-test env-var race: another
+    // non-`TEST_ENV_LOCK` test mutating `OPENHUMAN_WORKSPACE` in the await
+    // window flipped the reloaded config, intermittently failing
+    // `factory_routes_through_direct_when_mode_is_direct`. The factory reads
+    // mode + session purely from the passed `Config` (the auth-store path is
+    // derived from the config's own paths, not the env var), so pointing
+    // those at a fresh tempdir is fully isolated, deterministic, and needs
+    // no env mutation / `TEST_ENV_LOCK` / async.
+    #[test]
+    fn factory_routes_through_backend_when_mode_is_backend() {
         let tmp = tempfile::tempdir().expect("tempdir");
-        unsafe {
-            std::env::set_var("OPENHUMAN_WORKSPACE", tmp.path());
-        }
-
-        let mut config = Config::default();
+        let mut config = Config::default(); // composio.mode defaults to "backend"
         config.config_path = tmp.path().join("config.toml");
         config.workspace_dir = tmp.path().join("workspace");
-        config.save().await.expect("save fake config to disk");
 
-        let tool = ComposioActionTool::new(
-            Arc::new(config),
-            "GMAIL_FETCH_EMAILS".to_string(),
-            "read-shaped slug so sandbox/scope gates don't short-circuit \
-             the dispatch site"
-                .to_string(),
-            None,
-        );
-        let result = tool.execute(serde_json::json!({})).await.unwrap();
-        assert!(result.is_error, "no backend session must error");
-        let msg = error_text(&result);
+        // `ComposioClientKind` isn't `Debug`, so match rather than
+        // `expect_err` (which would need to format the unexpected `Ok`).
+        let msg = match crate::openhuman::composio::client::create_composio_client(&config) {
+            Ok(_) => panic!("backend mode with no session must error, but a client resolved"),
+            Err(e) => e.to_string(),
+        };
         assert!(
             msg.contains("backend") || msg.contains("session"),
             "expected backend-mode session error, got: {msg}"
@@ -433,59 +419,29 @@ mod tests {
             !msg.contains("direct mode"),
             "backend-mode failure must not surface direct-mode artifacts: {msg}"
         );
-
-        unsafe {
-            std::env::remove_var("OPENHUMAN_WORKSPACE");
-        }
     }
 
-    #[tokio::test]
-    async fn factory_routes_through_direct_when_mode_is_direct() {
-        // Direct-mode config with an inline api_key — factory resolves
-        // to the `Direct` variant. The downstream call will fail when
-        // it attempts to hit `backend.composio.dev` from the unit test
-        // sandbox, but the error must come from the direct path, not
-        // a backend session lookup.
-        //
-        // Production `.execute(..)` calls `load_config_with_timeout()`
-        // per call which reads from disk — see the matching note on
-        // `factory_routes_through_backend_when_mode_is_backend`.
-        use crate::openhuman::config::TEST_ENV_LOCK;
-        let _env_guard = TEST_ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
-
+    #[test]
+    fn factory_routes_through_direct_when_mode_is_direct() {
         let tmp = tempfile::tempdir().expect("tempdir");
-        unsafe {
-            std::env::set_var("OPENHUMAN_WORKSPACE", tmp.path());
-        }
-
         let mut config = Config::default();
         config.config_path = tmp.path().join("config.toml");
         config.workspace_dir = tmp.path().join("workspace");
         config.composio.mode = crate::openhuman::config::schema::COMPOSIO_MODE_DIRECT.to_string();
         config.composio.api_key = Some("test-direct-key".to_string());
-        config.save().await.expect("save fake config to disk");
 
-        let tool = ComposioActionTool::new(
-            Arc::new(config),
-            "GMAIL_FETCH_EMAILS".to_string(),
-            "read-shaped slug".to_string(),
-            None,
-        );
-        let result = tool.execute(serde_json::json!({})).await.unwrap();
-        // Direct-mode resolve succeeds → no `factory failed` error.
-        // The error (if any) will come from the downstream HTTP call,
-        // which is fine — we just need to confirm the dispatch routed
-        // through the direct branch rather than the backend branch.
-        let msg = error_text(&result);
+        // Direct mode + an api key must resolve to the Direct variant —
+        // never the backend branch. (Deterministic: pure factory call, no
+        // env / reload / await; see the note on the backend test.)
+        let kind = crate::openhuman::composio::client::create_composio_client(&config)
+            .expect("direct mode with an api key must resolve");
         assert!(
-            !msg.contains("no backend session") && !msg.contains("staging-api"),
-            "direct-mode dispatch must not leak backend session / staging-api \
-             artifacts: {msg}"
+            matches!(
+                kind,
+                crate::openhuman::composio::client::ComposioClientKind::Direct(_)
+            ),
+            "direct-mode config must route to the Direct client, not backend"
         );
-
-        unsafe {
-            std::env::remove_var("OPENHUMAN_WORKSPACE");
-        }
     }
 
     #[tokio::test]
diff --git a/src/openhuman/config/ops.rs b/src/openhuman/config/ops.rs
index 126b0ad68..644d9242b 100644
--- a/src/openhuman/config/ops.rs
+++ b/src/openhuman/config/ops.rs
@@ -496,6 +496,13 @@ pub async fn apply_model_settings(
     }
 
     config.save().await.map_err(|e| e.to_string())?;
+    // #1574 §4: the AIPanel workload matrix changes the embedder via THIS
+    // (model-settings) path — `embeddings_provider` above — not the
+    // memory-settings path. Trigger the same idempotent re-embed backfill
+    // so a UI embedder switch recovers prior memory under the new
+    // signature. Coverage-gated + non-fatal: if the active signature did
+    // not actually change, this enqueues nothing.
+    crate::openhuman::memory::tree::jobs::ensure_reembed_backfill(config);
     let snapshot = snapshot_config_json(config)?;
     Ok(RpcOutcome::new(
         snapshot,
@@ -539,6 +546,13 @@ pub async fn apply_memory_settings(
         }
     }
     config.save().await.map_err(|e| e.to_string())?;
+    // #1574 §4: the embedder may have just changed (provider/model/dims).
+    // Ensure a re-embed backfill chain exists for the new active signature
+    // so prior memory becomes retrievable again instead of silently going
+    // dark. Idempotent + non-fatal (covered space enqueues nothing; errors
+    // are logged, never fail the settings save). §7's migration is
+    // one-shot so it does not cover a later switch — this does.
+    crate::openhuman::memory::tree::jobs::ensure_reembed_backfill(config);
     let snapshot = snapshot_config_json(config)?;
     Ok(RpcOutcome::new(
         snapshot,
diff --git a/src/openhuman/embeddings/mod.rs b/src/openhuman/embeddings/mod.rs
index 783b24e36..e9c7130e8 100644
--- a/src/openhuman/embeddings/mod.rs
+++ b/src/openhuman/embeddings/mod.rs
@@ -28,7 +28,7 @@ pub use factory::{
 pub use noop::NoopEmbedding;
 pub use ollama::{OllamaEmbedding, DEFAULT_OLLAMA_DIMENSIONS, DEFAULT_OLLAMA_MODEL};
 pub use openai::OpenAiEmbedding;
-pub use provider_trait::EmbeddingProvider;
+pub use provider_trait::{format_embedding_signature, EmbeddingProvider};
 pub use store::{bytes_to_vec, cosine_similarity, vec_to_bytes, SearchResult, VectorStore};
 
 #[cfg(test)]
diff --git a/src/openhuman/embeddings/provider_trait.rs b/src/openhuman/embeddings/provider_trait.rs
index 6c194831b..262e1045f 100644
--- a/src/openhuman/embeddings/provider_trait.rs
+++ b/src/openhuman/embeddings/provider_trait.rs
@@ -2,6 +2,18 @@
 
 use async_trait::async_trait;
 
+/// Formats the canonical embedding-space signature string.
+///
+/// This is the **single source of truth** for the signature format. Both the
+/// live-provider [`EmbeddingProvider::signature`] and the config-derived
+/// `active_embedding_signature` (memory store factories) route through here so
+/// a signature computed from configuration is byte-identical to one computed
+/// from an instantiated provider. Drift between the two would silently split
+/// one embedding space into two (#1574).
+pub fn format_embedding_signature(name: &str, model_id: &str, dims: usize) -> String {
+    format!("provider={name};model={model_id};dims={dims}")
+}
+
 /// Interface for embedding providers that convert text into numerical vectors.
 #[async_trait]
 pub trait EmbeddingProvider: Send + Sync {
@@ -20,12 +32,7 @@ pub trait EmbeddingProvider: Send + Sync {
     /// comparable with newly-generated vectors and should be stored / queried
     /// separately by follow-up storage migrations.
     fn signature(&self) -> String {
-        format!(
-            "provider={};model={};dims={}",
-            self.name(),
-            self.model_id(),
-            self.dimensions()
-        )
+        format_embedding_signature(self.name(), self.model_id(), self.dimensions())
     }
 
     /// Generates embeddings for a batch of strings.
diff --git a/src/openhuman/memory/store/factories.rs b/src/openhuman/memory/store/factories.rs
index 8ce4a8818..08b50ba57 100644
--- a/src/openhuman/memory/store/factories.rs
+++ b/src/openhuman/memory/store/factories.rs
@@ -14,8 +14,8 @@ use std::sync::Arc;
 
 use crate::openhuman::config::{EmbeddingRouteConfig, MemoryConfig, StorageProviderConfig};
 use crate::openhuman::embeddings::{
-    self, EmbeddingProvider, DEFAULT_CLOUD_EMBEDDING_DIMENSIONS, DEFAULT_CLOUD_EMBEDDING_MODEL,
-    DEFAULT_OLLAMA_DIMENSIONS, DEFAULT_OLLAMA_MODEL,
+    self, format_embedding_signature, EmbeddingProvider, DEFAULT_CLOUD_EMBEDDING_DIMENSIONS,
+    DEFAULT_CLOUD_EMBEDDING_MODEL, DEFAULT_OLLAMA_DIMENSIONS, DEFAULT_OLLAMA_MODEL,
 };
 use crate::openhuman::memory::store::agentmemory::AgentMemoryBackend;
 use crate::openhuman::memory::store::unified::UnifiedMemory;
@@ -202,6 +202,25 @@ pub fn effective_embedding_settings(
     )
 }
 
+/// The **active embedding signature** — the canonical key every per-model
+/// sidecar read/write is scoped by (#1574).
+///
+/// Derived from [`effective_embedding_settings`] (the *intended*, non-probed
+/// selection) — deliberately **not** [`effective_embedding_settings_probed`].
+/// A transient Ollama-down fallback to cloud must never silently redefine the
+/// signature: that would re-key every read at a different space and trigger a
+/// spurious full re-embed on the next cold-Ollama launch (spec §3 oscillation
+/// guard). The string is produced by [`format_embedding_signature`], the same
+/// formatter [`EmbeddingProvider::signature`] uses, so a config-derived
+/// signature is byte-identical to a live provider's.
+pub fn active_embedding_signature(
+    memory: &MemoryConfig,
+    local_embedding_model: Option<&str>,
+) -> String {
+    let (provider, model, dims) = effective_embedding_settings(memory, local_embedding_model);
+    format_embedding_signature(&provider, &model, dims)
+}
+
 /// Async, health-checked variant of [`effective_embedding_settings`].
 ///
 /// If the intended provider is `"ollama"` but the daemon doesn't respond at
@@ -555,6 +574,43 @@ mod tests {
         );
     }
 
+    /// #1574 invariant: a config-derived `active_embedding_signature` MUST be
+    /// byte-identical to the live provider's `.signature()` for the same
+    /// (provider, model, dims). Drift here silently splits one embedding space
+    /// into two — copied/queried vectors would never match.
+    #[test]
+    fn active_signature_matches_live_provider_signature() {
+        for local in [None, Some("nomic-embed-text:latest"), Some("bge-m3")] {
+            let mem = MemoryConfig::default();
+            let (provider, model, dims) = effective_embedding_settings(&mem, local);
+            let live = embeddings::create_embedding_provider(&provider, &model, dims)
+                .expect("provider builds for test triple");
+            assert_eq!(
+                active_embedding_signature(&mem, local),
+                live.signature(),
+                "config-derived signature must equal live provider signature (local={local:?})"
+            );
+        }
+    }
+
+    #[test]
+    fn active_signature_ignores_probe_fallback() {
+        // active_embedding_signature keys off the *intended* selection
+        // (effective_embedding_settings), NOT the health-checked variant — so
+        // a transient Ollama-down fallback can't flip it to cloud. The dim is
+        // base/config-dependent (not what this test pins); the provider+model
+        // staying the intended ollama/bge-m3 is the probe-stability property.
+        let mem = MemoryConfig::default();
+        let sig = active_embedding_signature(&mem, Some("bge-m3"));
+        assert!(
+            sig.starts_with("provider=ollama;model=bge-m3;dims="),
+            "intended local selection must survive (no cloud fallback); got {sig}"
+        );
+        // And it must equal the non-probed settings, formatted identically.
+        let (p, m, d) = effective_embedding_settings(&mem, Some("bge-m3"));
+        assert_eq!(sig, format_embedding_signature(&p, &m, d));
+    }
+
     #[test]
     fn effective_memory_backend_name_always_returns_namespace() {
         assert_eq!(effective_memory_backend_name("sqlite", None), "namespace");
diff --git a/src/openhuman/memory/store/mod.rs b/src/openhuman/memory/store/mod.rs
index 740563a06..ba0366f88 100644
--- a/src/openhuman/memory/store/mod.rs
+++ b/src/openhuman/memory/store/mod.rs
@@ -28,8 +28,8 @@ pub use agentmemory::{agentmemory_default_url, AgentMemoryBackend, DEFAULT_AGENT
 
 pub use client::{MemoryClient, MemoryClientRef, MemoryState};
 pub use factories::{
-    create_memory, create_memory_for_migration, create_memory_with_local_ai,
-    create_memory_with_storage, create_memory_with_storage_and_routes,
+    active_embedding_signature, create_memory, create_memory_for_migration,
+    create_memory_with_local_ai, create_memory_with_storage, create_memory_with_storage_and_routes,
     effective_embedding_settings, effective_embedding_settings_probed,
     effective_memory_backend_name,
 };
diff --git a/src/openhuman/memory/tree/jobs/handlers/mod.rs b/src/openhuman/memory/tree/jobs/handlers/mod.rs
index ed0edfa93..d58766930 100644
--- a/src/openhuman/memory/tree/jobs/handlers/mod.rs
+++ b/src/openhuman/memory/tree/jobs/handlers/mod.rs
@@ -18,7 +18,8 @@ use crate::openhuman::memory::tree::content_store::{
 use crate::openhuman::memory::tree::jobs::store;
 use crate::openhuman::memory::tree::jobs::types::{
     AppendBufferPayload, AppendTarget, DigestDailyPayload, ExtractChunkPayload, FlushStalePayload,
-    Job, JobKind, JobOutcome, NewJob, NodeRef, SealPayload, TopicRoutePayload,
+    Job, JobKind, JobOutcome, NewJob, NodeRef, ReembedBackfillPayload, SealPayload,
+    TopicRoutePayload,
 };
 use crate::openhuman::memory::tree::score;
 use crate::openhuman::memory::tree::score::embed::{build_embedder_from_config, pack_checked};
@@ -45,6 +46,7 @@ pub async fn handle_job(config: &Config, job: &Job) -> Result<JobOutcome> {
         JobKind::TopicRoute => handle_topic_route(config, job).await,
         JobKind::DigestDaily => handle_digest_daily(config, job).await,
         JobKind::FlushStale => handle_flush_stale(config, job).await,
+        JobKind::ReembedBackfill => handle_reembed_backfill(config, job).await,
     }
 }
 
@@ -74,7 +76,7 @@ async fn handle_extract(config: &Config, job: &Job) -> Result<JobOutcome> {
 
     let scoring_cfg = score::ScoringConfig::from_config(config);
     let result = score::score_chunk(&chunk_with_body, &scoring_cfg).await?;
-    let packed_embedding = if result.kept {
+    let chunk_embedding: Option<Vec<f32>> = if result.kept {
         let embedder =
             build_embedder_from_config(config).context("build embedder in extract handler")?;
         // Reuse the body already read — avoid a second disk read.
@@ -82,10 +84,13 @@ async fn handle_extract(config: &Config, job: &Job) -> Result<JobOutcome> {
             .embed(&body)
             .await
             .with_context(|| format!("embed chunk_id={} in extract handler", chunk.id))?;
-        Some(
-            pack_checked(&vector)
-                .with_context(|| format!("pack embedding for chunk_id={}", chunk.id))?,
-        )
+        // Preserve the pre-cutover dimension guard (the job fails fast on a
+        // misconfigured embedder) even though #1574 no longer persists the
+        // packed blob to the legacy `mem_tree_chunks.embedding` column —
+        // the vector now goes to the per-model sidecar instead.
+        pack_checked(&vector)
+            .with_context(|| format!("validate embedding dims for chunk_id={}", chunk.id))?;
+        Some(vector)
     } else {
         None
     };
@@ -117,6 +122,9 @@ async fn handle_extract(config: &Config, job: &Job) -> Result<JobOutcome> {
         None
     };
 
+    // #1574: resolve the active embedding signature once (probe-stable,
+    // config-derived) so the sidecar write below is keyed correctly.
+    let active_sig = chunk_store::tree_active_signature(config);
     let (did_enqueue_source, did_enqueue_route) = chunk_store::with_connection(config, |conn| {
         let tx = conn.unchecked_transaction()?;
         score::persist_score_tx(
@@ -129,15 +137,24 @@ async fn handle_extract(config: &Config, job: &Job) -> Result<JobOutcome> {
         if result.kept {
             tx.execute(
                 "UPDATE mem_tree_chunks
-                        SET embedding = ?1,
-                            lifecycle_status = ?2
-                      WHERE id = ?3",
-                rusqlite::params![
-                    packed_embedding,
-                    chunk_store::CHUNK_STATUS_ADMITTED,
-                    chunk.id,
-                ],
+                        SET lifecycle_status = ?1
+                      WHERE id = ?2",
+                rusqlite::params![chunk_store::CHUNK_STATUS_ADMITTED, chunk.id],
             )?;
+            // #1574 write-side cutover: persist the embedding to the
+            // per-model `mem_tree_chunk_embeddings` sidecar at the active
+            // signature, inside THIS tx so it commits atomically with the
+            // lifecycle / score / job-enqueue writes. The legacy
+            // `mem_tree_chunks.embedding` column is no longer written
+            // (left intact for the §7 one-shot migration to read).
+            if let Some(emb) = chunk_embedding.as_deref() {
+                chunk_store::set_chunk_embedding_for_signature_tx(
+                    &tx,
+                    &chunk.id,
+                    &active_sig,
+                    emb,
+                )?;
+            }
         } else {
             tx.execute(
                 "UPDATE mem_tree_chunks
@@ -525,6 +542,156 @@ async fn handle_flush_stale(config: &Config, job: &Job) -> Result<JobOutcome> {
     Ok(JobOutcome::Done)
 }
 
+/// Texts per `ReembedBackfill` run. Bounded so one run holds the global
+/// single-LLM-slot (the job is `is_llm_bound`) for a predictable spell —
+/// the laptop-RAM safety the local-LLM-load rule requires. The chain
+/// self-continues via `Defer` until no rows remain.
+const REEMBED_BACKFILL_BATCH: usize = 16;
+/// Delay before the deferred chain revisits this same job row.
+const REEMBED_BACKFILL_REVISIT_MS: i64 = 750;
+
+/// #1574 §6: re-embed a bounded batch of chunks/summaries that lack a
+/// vector at the **active** signature, then `Defer` to revisit until the
+/// space is fully covered. Sources: the §7 dim-mismatch slice and any
+/// embedder switch (post-switch every prior row is missing at the new
+/// signature). One chain per signature (dedupe key); self-continues via
+/// `Defer` (reschedules this row — no re-enqueue, no dedupe race).
+///
+/// Per-row read/embed failures are logged and skipped, never fail the
+/// chain — one unreadable row must not strand the rest of memory.
+async fn handle_reembed_backfill(config: &Config, job: &Job) -> Result<JobOutcome> {
+    let payload: ReembedBackfillPayload =
+        serde_json::from_str(&job.payload_json).context("parse ReembedBackfill payload")?;
+    let active_sig = chunk_store::tree_active_signature(config);
+    if active_sig != payload.signature {
+        // The embedder changed since this chain started; a fresh chain for
+        // the new signature supersedes it. Finish this stale one.
+        log::info!(
+            "[memory_tree::jobs] reembed_backfill: stale signature (job sig={}, active={active_sig}); finishing",
+            payload.signature
+        );
+        return Ok(JobOutcome::Done);
+    }
+
+    // Phase 1 (short read): up to BATCH ids lacking a sidecar vector at the
+    // active signature — chunks first, then summaries to fill the batch.
+    let (chunk_ids, summary_ids): (Vec<String>, Vec<String>) =
+        chunk_store::with_connection(config, |conn| {
+            let chunks: Vec<String> = {
+                let mut stmt = conn.prepare(
+                    "SELECT id FROM mem_tree_chunks c
+                      WHERE NOT EXISTS (
+                          SELECT 1 FROM mem_tree_chunk_embeddings e
+                           WHERE e.chunk_id = c.id AND e.model_signature = ?1)
+                      LIMIT ?2",
+                )?;
+                let ids = stmt
+                    .query_map(
+                        rusqlite::params![active_sig, REEMBED_BACKFILL_BATCH as i64],
+                        |r| r.get::<_, String>(0),
+                    )?
+                    .collect::<rusqlite::Result<Vec<String>>>()?;
+                ids
+            };
+            let remaining = REEMBED_BACKFILL_BATCH.saturating_sub(chunks.len());
+            let summaries: Vec<String> = if remaining == 0 {
+                Vec::new()
+            } else {
+                let mut stmt = conn.prepare(
+                    "SELECT id FROM mem_tree_summaries s
+                      WHERE s.deleted = 0 AND NOT EXISTS (
+                          SELECT 1 FROM mem_tree_summary_embeddings e
+                           WHERE e.summary_id = s.id AND e.model_signature = ?1)
+                      LIMIT ?2",
+                )?;
+                let ids = stmt
+                    .query_map(rusqlite::params![active_sig, remaining as i64], |r| {
+                        r.get::<_, String>(0)
+                    })?
+                    .collect::<rusqlite::Result<Vec<String>>>()?;
+                ids
+            };
+            Ok((chunks, summaries))
+        })?;
+
+    if chunk_ids.is_empty() && summary_ids.is_empty() {
+        crate::openhuman::memory::tree::jobs::set_backfill_in_progress(false);
+        log::info!(
+            "[memory_tree::jobs] reembed_backfill: sig={active_sig} fully covered; chain complete"
+        );
+        return Ok(JobOutcome::Done);
+    }
+    crate::openhuman::memory::tree::jobs::set_backfill_in_progress(true);
+
+    // Phase 2 (no tx held): embed each row's stored source text. Per-row
+    // errors are skipped (logged) so a single bad row can't strand memory.
+    let embedder =
+        build_embedder_from_config(config).context("build embedder in reembed_backfill")?;
+    let mut chunk_vecs: Vec<(String, Vec<f32>)> = Vec::new();
+    for id in &chunk_ids {
+        match content_read::read_chunk_body(config, id) {
+            Ok(body) => match embedder.embed(&body).await {
+                Ok(v) if pack_checked(&v).is_ok() => chunk_vecs.push((id.clone(), v)),
+                Ok(_) => log::warn!(
+                    "[memory_tree::jobs] reembed_backfill: chunk {id} embed wrong dim, skipping"
+                ),
+                Err(e) => log::warn!(
+                    "[memory_tree::jobs] reembed_backfill: chunk {id} embed failed: {e}; skipping"
+                ),
+            },
+            Err(e) => log::warn!(
+                "[memory_tree::jobs] reembed_backfill: chunk {id} body read failed: {e}; skipping"
+            ),
+        }
+    }
+    let mut summary_vecs: Vec<(String, Vec<f32>)> = Vec::new();
+    for id in &summary_ids {
+        match content_read::read_summary_body(config, id) {
+            Ok(body) => match embedder.embed(&body).await {
+                Ok(v) if pack_checked(&v).is_ok() => summary_vecs.push((id.clone(), v)),
+                Ok(_) => log::warn!(
+                    "[memory_tree::jobs] reembed_backfill: summary {id} embed wrong dim, skipping"
+                ),
+                Err(e) => log::warn!(
+                    "[memory_tree::jobs] reembed_backfill: summary {id} embed failed: {e}; skipping"
+                ),
+            },
+            Err(e) => log::warn!(
+                "[memory_tree::jobs] reembed_backfill: summary {id} body read failed: {e}; skipping"
+            ),
+        }
+    }
+
+    // Phase 3 (one short tx): persist all collected vectors to the sidecar.
+    chunk_store::with_connection(config, |conn| {
+        let tx = conn.unchecked_transaction()?;
+        for (id, v) in &chunk_vecs {
+            chunk_store::set_chunk_embedding_for_signature_tx(&tx, id, &active_sig, v)?;
+        }
+        for (id, v) in &summary_vecs {
+            crate::openhuman::memory::tree::tree_source::store::set_summary_embedding_for_signature_tx(
+                &tx, id, &active_sig, v,
+            )?;
+        }
+        tx.commit()?;
+        Ok(())
+    })?;
+
+    log::info!(
+        "[memory_tree::jobs] reembed_backfill: sig={active_sig} embedded chunks={} summaries={} (scanned c={} s={}); revisiting",
+        chunk_vecs.len(),
+        summary_vecs.len(),
+        chunk_ids.len(),
+        summary_ids.len()
+    );
+    // More rows may remain (this batch was bounded). Reschedule THIS row —
+    // no re-enqueue, so the per-signature dedupe key stays valid.
+    Ok(JobOutcome::Defer {
+        until_ms: chrono::Utc::now().timestamp_millis() + REEMBED_BACKFILL_REVISIT_MS,
+        reason: "#1574 §6 re-embed backfill: batch done, more pending".to_string(),
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -880,4 +1047,171 @@ mod tests {
         // No new jobs should have been enqueued (buffer didn't cross gate).
         assert_eq!(count_total(&cfg).unwrap(), pre);
     }
+
+    /// #1574 §6: a chunk with content but no sidecar vector at the active
+    /// signature (the post-switch / dim-mismatch state) is re-embedded by
+    /// `handle_reembed_backfill`; the chain `Defer`s while work remains and
+    /// returns `Done` once the space is covered; a stale-signature job
+    /// finishes immediately without touching anything.
+    ///
+    /// (The process-global `backfill_in_progress` flag is intentionally not
+    /// asserted here — it is shared across parallel tests and set widely by
+    /// the §7 trigger, so asserting it would be flaky. The handler's
+    /// deterministic effects are what this test pins.)
+    #[tokio::test]
+    async fn reembed_backfill_repopulates_then_completes() {
+        use crate::openhuman::memory::tree::store::{
+            get_chunk_embedding_for_signature, tree_active_signature, upsert_chunks,
+            upsert_staged_chunks_tx,
+        };
+        use crate::openhuman::memory::tree::types::{
+            chunk_id, Chunk, Metadata, SourceKind, SourceRef,
+        };
+
+        let (_tmp, cfg) = test_config();
+        let ts = chrono::Utc.timestamp_millis_opt(1_700_000_000_000).unwrap();
+        let chunk = Chunk {
+            id: chunk_id(SourceKind::Chat, "slack:#eng", 0, "reembed-seed"),
+            content: "memory content about the phoenix migration project".into(),
+            metadata: Metadata {
+                source_kind: SourceKind::Chat,
+                source_id: "slack:#eng".into(),
+                owner: "alice".into(),
+                timestamp: ts,
+                time_range: (ts, ts),
+                tags: vec![],
+                source_ref: Some(SourceRef::new("slack://x")),
+            },
+            token_count: 12,
+            seq_in_source: 0,
+            created_at: ts,
+            partial_message: false,
+        };
+        upsert_chunks(&cfg, &[chunk.clone()]).unwrap();
+        // Stage the body to disk so `read_chunk_body` succeeds in the handler.
+        let content_root = cfg.memory_tree_content_root();
+        std::fs::create_dir_all(&content_root).unwrap();
+        let staged = content_store::stage_chunks(&content_root, &[chunk.clone()]).unwrap();
+        with_connection(&cfg, |conn| {
+            let tx = conn.unchecked_transaction()?;
+            upsert_staged_chunks_tx(&tx, &staged)?;
+            tx.commit()?;
+            Ok(())
+        })
+        .unwrap();
+
+        let sig = tree_active_signature(&cfg);
+        assert!(
+            get_chunk_embedding_for_signature(&cfg, &chunk.id, &sig)
+                .unwrap()
+                .is_none(),
+            "precondition: no sidecar vector at the active signature"
+        );
+
+        // Work present → re-embed + write sidecar, Defer to revisit.
+        let job = mk_running_job(
+            JobKind::ReembedBackfill,
+            serde_json::to_string(&ReembedBackfillPayload {
+                signature: sig.clone(),
+            })
+            .unwrap(),
+        );
+        let out = handle_reembed_backfill(&cfg, &job).await.unwrap();
+        assert!(
+            matches!(out, JobOutcome::Defer { .. }),
+            "work present must Defer (self-continue), got {out:?}"
+        );
+        assert!(
+            get_chunk_embedding_for_signature(&cfg, &chunk.id, &sig)
+                .unwrap()
+                .is_some(),
+            "chunk re-embedded into the sidecar at the active signature"
+        );
+
+        // Nothing left → Done.
+        let out2 = handle_reembed_backfill(&cfg, &job).await.unwrap();
+        assert_eq!(out2, JobOutcome::Done, "covered space must complete");
+
+        // Stale signature (embedder changed since enqueue) → finishes
+        // immediately, no work, no panic.
+        let stale = mk_running_job(
+            JobKind::ReembedBackfill,
+            serde_json::to_string(&ReembedBackfillPayload {
+                signature: "provider=other;model=x;dims=1".into(),
+            })
+            .unwrap(),
+        );
+        assert_eq!(
+            handle_reembed_backfill(&cfg, &stale).await.unwrap(),
+            JobOutcome::Done
+        );
+    }
+
+    /// #1574 §4: `ensure_reembed_backfill` (the switch-path trigger) enqueues
+    /// exactly one chain when there is uncovered work, is idempotent on
+    /// re-call (per-signature dedupe), and enqueues nothing for an
+    /// empty/covered space.
+    #[tokio::test]
+    async fn ensure_reembed_backfill_enqueues_only_when_uncovered() {
+        use crate::openhuman::memory::tree::jobs::ensure_reembed_backfill;
+        use crate::openhuman::memory::tree::store::{upsert_chunks, upsert_staged_chunks_tx};
+        use crate::openhuman::memory::tree::types::{
+            chunk_id, Chunk, Metadata, SourceKind, SourceRef,
+        };
+
+        // Empty space → nothing to do → no job.
+        let (_t0, empty_cfg) = test_config();
+        ensure_reembed_backfill(&empty_cfg);
+        assert_eq!(
+            count_jobs_of_kind(&empty_cfg, "reembed_backfill"),
+            0,
+            "empty/covered space must not enqueue a backfill"
+        );
+
+        // Chunk with content but no sidecar vector → exactly one chain.
+        let (_t1, cfg) = test_config();
+        let ts = chrono::Utc.timestamp_millis_opt(1_700_000_000_000).unwrap();
+        let chunk = Chunk {
+            id: chunk_id(SourceKind::Chat, "slack:#eng", 0, "ensure-seed"),
+            content: "memory content needing a re-embed".into(),
+            metadata: Metadata {
+                source_kind: SourceKind::Chat,
+                source_id: "slack:#eng".into(),
+                owner: "alice".into(),
+                timestamp: ts,
+                time_range: (ts, ts),
+                tags: vec![],
+                source_ref: Some(SourceRef::new("slack://x")),
+            },
+            token_count: 12,
+            seq_in_source: 0,
+            created_at: ts,
+            partial_message: false,
+        };
+        upsert_chunks(&cfg, &[chunk.clone()]).unwrap();
+        let content_root = cfg.memory_tree_content_root();
+        std::fs::create_dir_all(&content_root).unwrap();
+        let staged = content_store::stage_chunks(&content_root, &[chunk.clone()]).unwrap();
+        with_connection(&cfg, |conn| {
+            let tx = conn.unchecked_transaction()?;
+            upsert_staged_chunks_tx(&tx, &staged)?;
+            tx.commit()?;
+            Ok(())
+        })
+        .unwrap();
+
+        ensure_reembed_backfill(&cfg);
+        assert_eq!(
+            count_jobs_of_kind(&cfg, "reembed_backfill"),
+            1,
+            "uncovered work must enqueue exactly one backfill chain"
+        );
+        // Idempotent — re-call must not create a second chain (dedupe by sig).
+        ensure_reembed_backfill(&cfg);
+        assert_eq!(
+            count_jobs_of_kind(&cfg, "reembed_backfill"),
+            1,
+            "re-call must dedupe to a single chain per signature"
+        );
+    }
 }
diff --git a/src/openhuman/memory/tree/jobs/mod.rs b/src/openhuman/memory/tree/jobs/mod.rs
index 77e8287f2..7550e98ce 100644
--- a/src/openhuman/memory/tree/jobs/mod.rs
+++ b/src/openhuman/memory/tree/jobs/mod.rs
@@ -33,6 +33,96 @@ pub mod testing;
 pub mod types;
 mod worker;
 
+use std::sync::atomic::{AtomicBool, Ordering};
+
+/// #1574 §6 / #1365: set while a re-embed backfill chain has work pending.
+///
+/// Read by the first-person / subconscious retrieval layer so an empty
+/// vector-search result during the backfill window is interpreted as
+/// "not searched yet" rather than "no such memory" — preventing the agent
+/// from confidently asserting false self-ignorance mid-re-embed. Set true
+/// when a backfill is enqueued / still has rows; cleared when the chain
+/// drains. Process-global (resets to false on restart; the worker re-sets
+/// it on the next backfill tick — acceptable for v1).
+static BACKFILL_IN_PROGRESS: AtomicBool = AtomicBool::new(false);
+
+/// Mark whether a re-embed backfill currently has pending work.
+pub fn set_backfill_in_progress(v: bool) {
+    BACKFILL_IN_PROGRESS.store(v, Ordering::Relaxed);
+}
+
+/// True while a re-embed backfill chain still has rows to process. The
+/// #1365 absence-reasoning consumer checks this before treating an empty
+/// semantic-recall result as "no memory exists".
+pub fn backfill_in_progress() -> bool {
+    BACKFILL_IN_PROGRESS.load(Ordering::Relaxed)
+}
+
+/// #1574 §4: ensure a re-embed backfill chain exists for the **current**
+/// active signature, if (and only if) there is uncovered work.
+///
+/// This is the switch-path trigger: call it after the embedder config
+/// changes (a new signature → every prior row is missing at it). The §7
+/// migration is one-shot (`user_version`-gated) so it does NOT fire on a
+/// later model switch — without this, switching silently blinds prior
+/// memory. Standalone (own connection); the §7 migration keeps its own
+/// in-tx enqueue (atomic with the copy). Idempotent + non-fatal: the
+/// per-signature dedupe key means at most one chain per space, and a
+/// covered space enqueues nothing. Errors are logged, never propagated —
+/// a failed enqueue must not fail the user's settings save.
+pub fn ensure_reembed_backfill(config: &crate::openhuman::config::Config) {
+    let sig = crate::openhuman::memory::tree::store::tree_active_signature(config);
+    let result = crate::openhuman::memory::tree::store::with_connection(config, |conn| {
+        let has_uncovered: bool = conn.query_row(
+            "SELECT EXISTS(
+                 SELECT 1 FROM mem_tree_chunks c
+                  WHERE NOT EXISTS (SELECT 1 FROM mem_tree_chunk_embeddings e
+                                     WHERE e.chunk_id = c.id AND e.model_signature = ?1))
+               OR EXISTS(
+                 SELECT 1 FROM mem_tree_summaries s
+                  WHERE s.deleted = 0 AND NOT EXISTS (SELECT 1 FROM mem_tree_summary_embeddings e
+                                     WHERE e.summary_id = s.id AND e.model_signature = ?1))",
+            rusqlite::params![sig],
+            |r| r.get(0),
+        )?;
+        Ok(has_uncovered)
+    });
+    match result {
+        Ok(true) => {
+            let job = match types::NewJob::reembed_backfill(&types::ReembedBackfillPayload {
+                signature: sig.clone(),
+            }) {
+                Ok(j) => j,
+                Err(e) => {
+                    log::warn!(
+                        "[memory_tree::jobs] ensure_reembed_backfill: build job failed: {e}"
+                    );
+                    return;
+                }
+            };
+            match store::enqueue(config, &job) {
+                Ok(_) => {
+                    set_backfill_in_progress(true);
+                    log::info!(
+                        "[memory_tree::jobs] ensure_reembed_backfill: enqueued chain for sig={sig}"
+                    );
+                }
+                Err(e) => log::warn!(
+                    "[memory_tree::jobs] ensure_reembed_backfill: enqueue failed for sig={sig}: {e}"
+                ),
+            }
+        }
+        Ok(false) => {
+            log::debug!(
+                "[memory_tree::jobs] ensure_reembed_backfill: sig={sig} fully covered; nothing to do"
+            );
+        }
+        Err(e) => log::warn!(
+            "[memory_tree::jobs] ensure_reembed_backfill: coverage probe failed for sig={sig}: {e}"
+        ),
+    }
+}
+
 pub use scheduler::{backfill_missing_digests, trigger_digest};
 pub use store::{
     claim_next, count_by_status, count_total, enqueue, enqueue_tx, get_job, mark_deferred,
diff --git a/src/openhuman/memory/tree/jobs/types.rs b/src/openhuman/memory/tree/jobs/types.rs
index 6aaab3582..8b1598d02 100644
--- a/src/openhuman/memory/tree/jobs/types.rs
+++ b/src/openhuman/memory/tree/jobs/types.rs
@@ -24,6 +24,10 @@ pub enum JobKind {
     DigestDaily,
     /// Walk stale buffers and enqueue `Seal` jobs for any over the age cap.
     FlushStale,
+    /// #1574 §6: re-embed a bounded batch of chunks/summaries that lack a
+    /// vector at the active embedding signature (post model-switch, or the
+    /// §7 dim-mismatch slice), then self-continue until none remain.
+    ReembedBackfill,
 }
 
 impl JobKind {
@@ -36,6 +40,7 @@ impl JobKind {
             JobKind::TopicRoute => "topic_route",
             JobKind::DigestDaily => "digest_daily",
             JobKind::FlushStale => "flush_stale",
+            JobKind::ReembedBackfill => "reembed_backfill",
         }
     }
 
@@ -48,6 +53,7 @@ impl JobKind {
             "topic_route" => JobKind::TopicRoute,
             "digest_daily" => JobKind::DigestDaily,
             "flush_stale" => JobKind::FlushStale,
+            "reembed_backfill" => JobKind::ReembedBackfill,
             other => return Err(anyhow!("unknown JobKind '{other}'")),
         })
     }
@@ -60,7 +66,11 @@ impl JobKind {
     pub fn is_llm_bound(&self) -> bool {
         matches!(
             self,
-            JobKind::ExtractChunk | JobKind::Seal | JobKind::DigestDaily | JobKind::TopicRoute
+            JobKind::ExtractChunk
+                | JobKind::Seal
+                | JobKind::DigestDaily
+                | JobKind::TopicRoute
+                | JobKind::ReembedBackfill
         )
     }
 }
@@ -267,6 +277,26 @@ impl FlushStalePayload {
     }
 }
 
+/// #1574 §6 re-embed backfill. One chain per embedding signature: the
+/// `dedupe_key` is the signature, so re-triggering while a chain is
+/// in-flight is correctly suppressed (exactly one backfill per space).
+/// The handler self-continues via `JobOutcome::Defer` (reschedules this
+/// same row) rather than re-enqueuing, so the fixed dedupe key is safe.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct ReembedBackfillPayload {
+    /// The embedding signature this chain re-embeds under. If the active
+    /// signature has since changed, the handler treats this job as stale
+    /// and finishes (a fresh chain for the new signature takes over).
+    pub signature: String,
+}
+
+impl ReembedBackfillPayload {
+    /// Stable dedupe key — one in-flight backfill chain per signature.
+    pub fn dedupe_key(&self) -> String {
+        format!("reembed_backfill:{}", self.signature)
+    }
+}
+
 /// One row in `mem_tree_jobs`. `payload_json` is left as a raw string so
 /// callers parse it lazily based on `kind`.
 #[derive(Clone, Debug)]
@@ -365,6 +395,17 @@ impl NewJob {
             max_attempts: None,
         })
     }
+
+    /// Build a [`JobKind::ReembedBackfill`] enqueue request (#1574 §6).
+    pub fn reembed_backfill(p: &ReembedBackfillPayload) -> Result<Self> {
+        Ok(Self {
+            kind: JobKind::ReembedBackfill,
+            payload_json: serde_json::to_string(p)?,
+            dedupe_key: Some(p.dedupe_key()),
+            available_at_ms: None,
+            max_attempts: None,
+        })
+    }
 }
 
 #[cfg(test)]
@@ -380,6 +421,7 @@ mod tests {
             JobKind::TopicRoute,
             JobKind::DigestDaily,
             JobKind::FlushStale,
+            JobKind::ReembedBackfill,
         ] {
             assert_eq!(JobKind::parse(k.as_str()).unwrap(), k);
         }
@@ -454,6 +496,7 @@ mod tests {
         assert!(JobKind::Seal.is_llm_bound());
         assert!(JobKind::DigestDaily.is_llm_bound());
         assert!(JobKind::TopicRoute.is_llm_bound());
+        assert!(JobKind::ReembedBackfill.is_llm_bound());
         assert!(!JobKind::AppendBuffer.is_llm_bound());
         assert!(!JobKind::FlushStale.is_llm_bound());
     }
diff --git a/src/openhuman/memory/tree/retrieval/drill_down.rs b/src/openhuman/memory/tree/retrieval/drill_down.rs
index f5190f324..c131f4c87 100644
--- a/src/openhuman/memory/tree/retrieval/drill_down.rs
+++ b/src/openhuman/memory/tree/retrieval/drill_down.rs
@@ -544,9 +544,9 @@ mod tests {
         with_connection(cfg, |conn| {
             let tx = conn.unchecked_transaction()?;
             tree_store::insert_tree_conn(&tx, &tree)?;
-            tree_store::insert_summary_tx(&tx, &l1_a, None)?;
-            tree_store::insert_summary_tx(&tx, &l1_b, None)?;
-            tree_store::insert_summary_tx(&tx, &root, None)?;
+            tree_store::insert_summary_tx(&tx, &l1_a, None, "test")?;
+            tree_store::insert_summary_tx(&tx, &l1_b, None, "test")?;
+            tree_store::insert_summary_tx(&tx, &root, None, "test")?;
             tx.commit()?;
             Ok(())
         })
diff --git a/src/openhuman/memory/tree/retrieval/integration_test.rs b/src/openhuman/memory/tree/retrieval/integration_test.rs
index 3fd58822e..11291c1bd 100644
--- a/src/openhuman/memory/tree/retrieval/integration_test.rs
+++ b/src/openhuman/memory/tree/retrieval/integration_test.rs
@@ -271,11 +271,19 @@ async fn seal_populates_summary_embedding() {
     .unwrap();
     assert_eq!(sealed.len(), 1, "expected one seal at the budget crossing");
 
+    // #1574 cutover: the seal path no longer writes the legacy
+    // `mem_tree_summaries.embedding` column — the vector is persisted to the
+    // per-model sidecar at the active signature inside the seal tx. Assert
+    // it round-trips through the public accessor (which reads the sidecar at
+    // the active signature), validating the write-side cutover end to end.
     let summary = src_store::get_summary(&cfg, &sealed[0]).unwrap().unwrap();
-    let emb = summary
-        .embedding
-        .as_ref()
-        .expect("sealed summary must have embedding");
+    assert!(
+        summary.embedding.is_none(),
+        "legacy summary embedding column must be NULL post-cutover"
+    );
+    let emb = src_store::get_summary_embedding(&cfg, &sealed[0])
+        .unwrap()
+        .expect("sealed summary must have an embedding in the per-model sidecar");
     assert_eq!(emb.len(), EMBEDDING_DIM);
 }
 
diff --git a/src/openhuman/memory/tree/retrieval/topic.rs b/src/openhuman/memory/tree/retrieval/topic.rs
index c87353093..7c049c0bb 100644
--- a/src/openhuman/memory/tree/retrieval/topic.rs
+++ b/src/openhuman/memory/tree/retrieval/topic.rs
@@ -590,7 +590,7 @@ mod tests {
         with_connection(&cfg, |conn| {
             let tx = conn.unchecked_transaction()?;
             tree_store::insert_tree_conn(&tx, &tree)?;
-            tree_store::insert_summary_tx(&tx, &summary, None)?;
+            tree_store::insert_summary_tx(&tx, &summary, None, "test")?;
             score_store::index_entities_tx(
                 &tx,
                 &[entity],
diff --git a/src/openhuman/memory/tree/rpc.rs b/src/openhuman/memory/tree/rpc.rs
index 5b2beff25..9d59a831e 100644
--- a/src/openhuman/memory/tree/rpc.rs
+++ b/src/openhuman/memory/tree/rpc.rs
@@ -256,6 +256,61 @@ pub async fn trigger_digest_rpc(
     ))
 }
 
+/// Response from the `memory_backfill_status` RPC (#1574 §4b). The frontend
+/// polls this while the re-embed modal is open to surface progress and to
+/// dismiss the modal once the new embedding space is fully covered.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct BackfillStatusResponse {
+    /// True while a re-embed backfill chain still has work pending — the
+    /// #1365 flag OR a queued/running `reembed_backfill` job.
+    pub in_progress: bool,
+    /// Count of `reembed_backfill` jobs in `ready` or `running` state. `0`
+    /// with `in_progress=false` means the active embedding space is fully
+    /// covered (modal can close).
+    pub pending_jobs: u64,
+}
+
+/// `memory_backfill_status` RPC handler (#1574 §4b). No inputs — reports
+/// whether a per-model re-embed backfill is in flight so the UI can warn
+/// the user that semantic recall is reduced until it drains.
+pub async fn backfill_status_rpc(
+    config: &Config,
+) -> Result<RpcOutcome<BackfillStatusResponse>, String> {
+    log::debug!("[memory_tree::rpc] backfill_status: entry");
+    // SQLite I/O off the async runtime thread, matching the sibling
+    // DB-backed handlers in this module (`get_chunk_rpc`, etc.).
+    let pending_jobs: u64 = tokio::task::spawn_blocking({
+        let config = config.clone();
+        move || {
+            store::with_connection(&config, |conn| {
+                let n: i64 = conn.query_row(
+                    "SELECT COUNT(*) FROM mem_tree_jobs
+                      WHERE kind = 'reembed_backfill' AND status IN ('ready', 'running')",
+                    [],
+                    |r| r.get(0),
+                )?;
+                Ok(n.max(0) as u64)
+            })
+        }
+    })
+    .await
+    .map_err(|e| format!("memory_backfill_status join error: {e}"))?
+    .map_err(|e| {
+        let msg = format!("memory_backfill_status: {e}");
+        log::debug!("[memory_tree::rpc] backfill_status: error: {msg}");
+        msg
+    })?;
+    let in_progress =
+        crate::openhuman::memory::tree::jobs::backfill_in_progress() || pending_jobs > 0;
+    Ok(RpcOutcome::single_log(
+        BackfillStatusResponse {
+            in_progress,
+            pending_jobs,
+        },
+        format!("memory_tree: backfill_status in_progress={in_progress} pending={pending_jobs}"),
+    ))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -327,4 +382,30 @@ mod tests {
         assert!(second.job_id.is_none());
         assert_eq!(count_total(&cfg).unwrap(), 1);
     }
+
+    /// #1574 §4b: `backfill_status_rpc` reports 0 pending on an idle space
+    /// and reflects a queued `reembed_backfill` job (forcing `in_progress`).
+    /// `in_progress` for the empty case is intentionally not asserted — the
+    /// underlying flag is a process-global shared across parallel tests.
+    #[tokio::test]
+    async fn backfill_status_reports_pending_jobs() {
+        use crate::openhuman::memory::tree::jobs;
+        let (_tmp, cfg) = test_config();
+
+        let s0 = backfill_status_rpc(&cfg).await.unwrap().value;
+        assert_eq!(s0.pending_jobs, 0, "idle space has no pending backfill");
+
+        let job = jobs::types::NewJob::reembed_backfill(&jobs::types::ReembedBackfillPayload {
+            signature: "provider=test;model=x;dims=1".into(),
+        })
+        .unwrap();
+        jobs::enqueue(&cfg, &job).unwrap();
+
+        let s1 = backfill_status_rpc(&cfg).await.unwrap().value;
+        assert_eq!(
+            s1.pending_jobs, 1,
+            "a ready reembed_backfill job must count"
+        );
+        assert!(s1.in_progress, "pending>0 forces in_progress=true");
+    }
 }
diff --git a/src/openhuman/memory/tree/schemas.rs b/src/openhuman/memory/tree/schemas.rs
index b4ff42519..a3caa22a3 100644
--- a/src/openhuman/memory/tree/schemas.rs
+++ b/src/openhuman/memory/tree/schemas.rs
@@ -30,6 +30,7 @@ pub fn all_controller_schemas() -> Vec<ControllerSchema> {
         schemas("list_chunks"),
         schemas("get_chunk"),
         schemas("trigger_digest"),
+        schemas("memory_backfill_status"),
         schemas("list_sources"),
         schemas("search"),
         schemas("recall"),
@@ -67,6 +68,10 @@ pub fn all_registered_controllers() -> Vec<RegisteredController> {
             schema: schemas("trigger_digest"),
             handler: handle_trigger_digest,
         },
+        RegisteredController {
+            schema: schemas("memory_backfill_status"),
+            handler: handle_memory_backfill_status,
+        },
         RegisteredController {
             schema: schemas("list_sources"),
             handler: handle_list_sources,
@@ -712,6 +717,32 @@ pub fn schemas(function: &str) -> ControllerSchema {
                 },
             ],
         },
+        "memory_backfill_status" => ControllerSchema {
+            namespace: NAMESPACE,
+            function: "memory_backfill_status",
+            description: "Report whether a per-model embedding re-embed \
+                backfill (#1574) is in flight. The UI polls this while the \
+                re-embed modal is open: semantic recall over not-yet-\
+                re-embedded memory is reduced until the chain drains.",
+            inputs: vec![],
+            outputs: vec![
+                FieldSchema {
+                    name: "in_progress",
+                    ty: TypeSchema::Bool,
+                    comment: "True while a re-embed backfill still has work \
+                        pending (flag set or a ready/running job).",
+                    required: true,
+                },
+                FieldSchema {
+                    name: "pending_jobs",
+                    ty: TypeSchema::U64,
+                    comment: "Count of reembed_backfill jobs in ready or \
+                        running state; 0 with in_progress=false means the \
+                        active embedding space is fully covered.",
+                    required: true,
+                },
+            ],
+        },
         _ => ControllerSchema {
             namespace: NAMESPACE,
             function: "unknown",
@@ -756,6 +787,13 @@ fn handle_trigger_digest(params: Map<String, Value>) -> ControllerFuture {
     })
 }
 
+fn handle_memory_backfill_status(_params: Map<String, Value>) -> ControllerFuture {
+    Box::pin(async move {
+        let config = config_rpc::load_config_with_timeout().await?;
+        to_json(tree_rpc::backfill_status_rpc(&config).await?)
+    })
+}
+
 // ── New read RPCs (Memory-tab UI) ────────────────────────────────────────
 
 fn handle_list_chunks(params: Map<String, Value>) -> ControllerFuture {
diff --git a/src/openhuman/memory/tree/store.rs b/src/openhuman/memory/tree/store.rs
index f0c8a5067..4b03e3a1a 100644
--- a/src/openhuman/memory/tree/store.rs
+++ b/src/openhuman/memory/tree/store.rs
@@ -43,6 +43,11 @@ pub const CHUNK_STATUS_SEALED: &str = "sealed";
 /// Chunk lifecycle: rejected by the admission gate (too low signal).
 pub const CHUNK_STATUS_DROPPED: &str = "dropped";
 
+/// `PRAGMA user_version` value once the one-shot legacy→sidecar embedding
+/// migration (#1574 §7) has run. `0` (fresh/legacy DB) triggers the copy on
+/// next open; `>= 1` skips it. Bump only for a new one-shot data migration.
+const TREE_EMBEDDING_MIGRATION_VERSION: i64 = 1;
+
 const SCHEMA: &str = "
 PRAGMA foreign_keys = ON;
 
@@ -776,9 +781,125 @@ pub(crate) fn with_connection<T>(
         "is_user",
         "INTEGER NOT NULL DEFAULT 0",
     )?;
+    // #1574 §7: one-shot, version-gated copy of legacy embedding columns
+    // into the per-model sidecar at the active signature. Runs once
+    // (PRAGMA user_version gate); cheap no-op on every subsequent open.
+    migrate_legacy_embeddings_to_sidecar(&conn, config)?;
     f(&conn)
 }
 
+/// One-shot migration (#1574 §7, vN): copy legacy `mem_tree_chunks.embedding`
+/// / `mem_tree_summaries.embedding` blobs into the per-model sidecar tables
+/// under the **active** signature, when (and only when) the legacy vector's
+/// dimensionality matches the active embedder's.
+///
+/// Version-gated via `PRAGMA user_version`: returns immediately once
+/// `>= TREE_EMBEDDING_MIGRATION_VERSION`, so the per-open cost is a single
+/// pragma read. Dim-mismatched rows are left for the §6 re-embed backfill —
+/// the blob's signature is unrecoverable (see spec §7b), so a same-length
+/// copy under the active signature is the only provably-safe move and
+/// anything else must be re-embedded. The legacy columns are **kept** (read
+/// here, dropped only in a later release — spec §7c). Idempotent: re-running
+/// before the version bumps re-copies the same rows harmlessly (sidecar
+/// upsert is ON CONFLICT); after the bump it is skipped entirely.
+fn migrate_legacy_embeddings_to_sidecar(conn: &Connection, config: &Config) -> Result<()> {
+    let version: i64 = conn
+        .query_row("PRAGMA user_version", [], |r| r.get(0))
+        .context("read PRAGMA user_version for #1574 migration")?;
+    if version >= TREE_EMBEDDING_MIGRATION_VERSION {
+        return Ok(());
+    }
+
+    let (provider, model, dims) = crate::openhuman::memory::store::effective_embedding_settings(
+        &config.memory,
+        config.workload_local_model("embeddings").as_deref(),
+    );
+    let sig = crate::openhuman::embeddings::format_embedding_signature(&provider, &model, dims);
+    log::info!(
+        "[memory_tree::migrate] #1574 §7: copying legacy embeddings → sidecar at sig={sig} (dims={dims})"
+    );
+
+    let tx = conn.unchecked_transaction()?;
+    let mut copied_chunks = 0usize;
+    let mut copied_summaries = 0usize;
+    let mut skipped_dim_mismatch = 0usize;
+
+    for (table, is_chunk) in [("mem_tree_chunks", true), ("mem_tree_summaries", false)] {
+        let mut stmt = tx.prepare(&format!(
+            "SELECT id, embedding FROM {table} WHERE embedding IS NOT NULL"
+        ))?;
+        let rows = stmt.query_map([], |r| {
+            Ok((r.get::<_, String>(0)?, r.get::<_, Vec<u8>>(1)?))
+        })?;
+        for row in rows {
+            let (id, blob) = row?;
+            if !blob.len().is_multiple_of(4) {
+                log::warn!(
+                    "[memory_tree::migrate] {table} id={id}: legacy blob len {} not /4, skipping",
+                    blob.len()
+                );
+                continue;
+            }
+            if blob.len() / 4 != dims {
+                // Different embedding space — unrecoverable from the blob.
+                // Leave for the §6 re-embed backfill.
+                skipped_dim_mismatch += 1;
+                continue;
+            }
+            let vec: Vec<f32> = blob
+                .chunks_exact(4)
+                .map(|c| f32::from_le_bytes([c[0], c[1], c[2], c[3]]))
+                .collect();
+            if is_chunk {
+                set_chunk_embedding_for_signature_tx(&tx, &id, &sig, &vec)?;
+                copied_chunks += 1;
+            } else {
+                crate::openhuman::memory::tree::tree_source::store::set_summary_embedding_for_signature_tx(
+                    &tx, &id, &sig, &vec,
+                )?;
+                copied_summaries += 1;
+            }
+        }
+    }
+
+    // #1574 §6: enqueue the re-embed backfill ONLY if there is genuinely
+    // uncovered work at the active signature (the dim-mismatch slice, or
+    // content-bearing rows with no vector). Gating this avoids queuing a
+    // no-op job on every DB open — which would otherwise pollute the jobs
+    // table for unrelated callers/tests. Enqueued atomically with the
+    // migration; dedupe key = signature, so exactly one chain per space.
+    let has_uncovered: bool = tx.query_row(
+        "SELECT EXISTS(
+             SELECT 1 FROM mem_tree_chunks c
+              WHERE NOT EXISTS (SELECT 1 FROM mem_tree_chunk_embeddings e
+                                 WHERE e.chunk_id = c.id AND e.model_signature = ?1))
+           OR EXISTS(
+             SELECT 1 FROM mem_tree_summaries s
+              WHERE s.deleted = 0 AND NOT EXISTS (SELECT 1 FROM mem_tree_summary_embeddings e
+                                 WHERE e.summary_id = s.id AND e.model_signature = ?1))",
+        rusqlite::params![sig],
+        |r| r.get(0),
+    )?;
+    if has_uncovered {
+        let backfill_job = crate::openhuman::memory::tree::jobs::types::NewJob::reembed_backfill(
+            &crate::openhuman::memory::tree::jobs::types::ReembedBackfillPayload {
+                signature: sig.clone(),
+            },
+        )?;
+        crate::openhuman::memory::tree::jobs::enqueue_tx(&tx, &backfill_job)?;
+        crate::openhuman::memory::tree::jobs::set_backfill_in_progress(true);
+    }
+
+    tx.commit()?;
+    conn.pragma_update(None, "user_version", TREE_EMBEDDING_MIGRATION_VERSION)
+        .context("set PRAGMA user_version after #1574 migration")?;
+    log::info!(
+        "[memory_tree::migrate] #1574 §7 done: copied chunks={copied_chunks} summaries={copied_summaries} \
+         skipped_dim_mismatch={skipped_dim_mismatch} (left for §6 re-embed); user_version={TREE_EMBEDDING_MIGRATION_VERSION}"
+    );
+    Ok(())
+}
+
 /// One pointer into the raw archive. A chunk's body is reconstructed by
 /// reading each [`RawRef`] in order and joining with `"\n\n"`.
 ///
@@ -945,31 +1066,45 @@ fn add_column_if_missing(conn: &Connection, table: &str, name: &str, sql_type: &
 
 // ── Phase 2: embedding column accessors ─────────────────────────────────
 
-/// Store a chunk's embedding as a packed little-endian `f32` blob.
-///
-/// Length is `embedding.len() * 4` bytes. The caller is responsible for
-/// ensuring all embeddings in a given deployment share the same dimension.
-pub fn set_chunk_embedding(config: &Config, chunk_id: &str, embedding: &[f32]) -> Result<()> {
-    let bytes: Vec<u8> = embedding.iter().flat_map(|f| f.to_le_bytes()).collect();
-    with_connection(config, |conn| {
-        let changed = conn.execute(
-            "UPDATE mem_tree_chunks SET embedding = ?1 WHERE id = ?2",
-            rusqlite::params![bytes, chunk_id],
-        )?;
-        if changed == 0 {
-            log::warn!("[memory_tree::store] set_chunk_embedding: no row for chunk_id={chunk_id}");
-        }
-        Ok(())
-    })
+/// Resolve the active embedding signature for the memory tree from the global
+/// [`Config`] — the canonical key every per-model sidecar read/write is scoped
+/// by (#1574). Reuses the established local-AI workload derivation
+/// ([`Config::workload_local_model`]) and the probe-stable
+/// `active_embedding_signature`; introduces no parallel resolution path.
+/// `pub(crate)` so the sibling `tree_source` summary store shares the exact
+/// same resolution.
+pub(crate) fn tree_active_signature(config: &Config) -> String {
+    let local_model = config.workload_local_model("embeddings");
+    crate::openhuman::memory::store::active_embedding_signature(
+        &config.memory,
+        local_model.as_deref(),
+    )
 }
 
-/// Store a chunk embedding for a specific provider/model/dimension signature.
+/// Store a chunk's embedding under the active model signature.
 ///
-/// This is the Stage-1 per-model table write path for #1574. The legacy
-/// `mem_tree_chunks.embedding` column is intentionally left untouched by this
-/// helper so callers can dual-write while query paths migrate.
-pub fn set_chunk_embedding_for_signature(
-    config: &Config,
+/// #1574 cutover: this now writes the per-model `mem_tree_chunk_embeddings`
+/// sidecar (via [`set_chunk_embedding_for_signature`]) instead of the legacy
+/// `mem_tree_chunks.embedding` column. Call sites are unchanged — the signature
+/// is resolved internally from `config`. The legacy column is left intact for
+/// the §7 one-shot migration to read; it is dropped only in a later release.
+pub fn set_chunk_embedding(config: &Config, chunk_id: &str, embedding: &[f32]) -> Result<()> {
+    let signature = tree_active_signature(config);
+    log::debug!(
+        "[memory_tree::store] set_chunk_embedding: chunk_id={chunk_id} sig={signature} dims={}",
+        embedding.len()
+    );
+    set_chunk_embedding_for_signature(config, chunk_id, &signature, embedding)
+}
+
+/// Core upsert into `mem_tree_chunk_embeddings` over an arbitrary
+/// `&Connection`. Shared by the standalone ([`set_chunk_embedding_for_signature`])
+/// and in-transaction ([`set_chunk_embedding_for_signature_tx`]) write paths so
+/// the SQL exists exactly once. `rusqlite::Transaction` derefs to `Connection`,
+/// so an in-tx caller passes `&tx` and the sidecar row commits atomically with
+/// the surrounding work (#1574 write-side cutover).
+fn upsert_chunk_embedding_conn(
+    conn: &rusqlite::Connection,
     chunk_id: &str,
     model_signature: &str,
     embedding: &[f32],
@@ -977,21 +1112,50 @@ pub fn set_chunk_embedding_for_signature(
     let bytes = embedding_to_blob(embedding);
     let dim = i64::try_from(embedding.len()).context("embedding dimension does not fit i64")?;
     let created_at = Utc::now().timestamp_millis() as f64 / 1000.0;
-    with_connection(config, |conn| {
-        conn.execute(
-            "INSERT INTO mem_tree_chunk_embeddings
+    conn.execute(
+        "INSERT INTO mem_tree_chunk_embeddings
              (chunk_id, model_signature, vector, dim, created_at)
              VALUES (?1, ?2, ?3, ?4, ?5)
              ON CONFLICT(chunk_id, model_signature) DO UPDATE SET
                 vector = excluded.vector,
                 dim = excluded.dim,
                 created_at = excluded.created_at",
-            rusqlite::params![chunk_id, model_signature, bytes, dim, created_at],
-        )?;
-        Ok(())
+        rusqlite::params![chunk_id, model_signature, bytes, dim, created_at],
+    )?;
+    Ok(())
+}
+
+/// Store a chunk embedding for a specific provider/model/dimension signature.
+///
+/// Per-model table write path for #1574. The legacy
+/// `mem_tree_chunks.embedding` column is intentionally left untouched by this
+/// helper (read by the §7 migration; dropped only in a later release).
+pub fn set_chunk_embedding_for_signature(
+    config: &Config,
+    chunk_id: &str,
+    model_signature: &str,
+    embedding: &[f32],
+) -> Result<()> {
+    with_connection(config, |conn| {
+        upsert_chunk_embedding_conn(conn, chunk_id, model_signature, embedding)
     })
 }
 
+/// Transaction-scoped variant of [`set_chunk_embedding_for_signature`].
+///
+/// For callers that already hold a `Transaction` (e.g. the chunk-admission
+/// handler, which commits the sidecar row in the SAME tx as the lifecycle
+/// + score + job-enqueue writes — #1574 write-side cutover). Opening a fresh
+/// connection there would break atomicity / deadlock on the busy DB.
+pub(crate) fn set_chunk_embedding_for_signature_tx(
+    tx: &rusqlite::Transaction<'_>,
+    chunk_id: &str,
+    model_signature: &str,
+    embedding: &[f32],
+) -> Result<()> {
+    upsert_chunk_embedding_conn(tx, chunk_id, model_signature, embedding)
+}
+
 /// Fetch a chunk embedding for exactly one provider/model/dimension signature.
 pub fn get_chunk_embedding_for_signature(
     config: &Config,
@@ -1015,32 +1179,17 @@ pub fn get_chunk_embedding_for_signature(
     })
 }
 
-/// Fetch a chunk's embedding, decoding the stored little-endian `f32` blob.
+/// Fetch a chunk's embedding for the active model signature.
 ///
-/// Returns `Ok(None)` if the chunk doesn't exist or has no embedding stored.
+/// #1574 cutover: reads the per-model `mem_tree_chunk_embeddings` sidecar at
+/// the active signature (via [`get_chunk_embedding_for_signature`]) instead of
+/// the legacy `mem_tree_chunks.embedding` column. Returns `Ok(None)` if the
+/// chunk has no vector under the active signature — e.g. during the §7
+/// backfill window, where this degrades retrieval gracefully (the row is
+/// simply absent from vector results, never cross-space compared).
 pub fn get_chunk_embedding(config: &Config, chunk_id: &str) -> Result<Option<Vec<f32>>> {
-    with_connection(config, |conn| {
-        let blob: Option<Option<Vec<u8>>> = conn
-            .query_row(
-                "SELECT embedding FROM mem_tree_chunks WHERE id = ?1",
-                rusqlite::params![chunk_id],
-                |r| r.get::<_, Option<Vec<u8>>>(0),
-            )
-            .optional()?;
-        match blob.flatten() {
-            None => Ok(None),
-            Some(bytes) => {
-                if !bytes.len().is_multiple_of(4) {
-                    anyhow::bail!("embedding blob length {} not a multiple of 4", bytes.len());
-                }
-                let floats: Vec<f32> = bytes
-                    .chunks_exact(4)
-                    .map(|c| f32::from_le_bytes([c[0], c[1], c[2], c[3]]))
-                    .collect();
-                Ok(Some(floats))
-            }
-        }
-    })
+    let signature = tree_active_signature(config);
+    get_chunk_embedding_for_signature(config, chunk_id, &signature)
 }
 
 fn embedding_to_blob(embedding: &[f32]) -> Vec<u8> {
diff --git a/src/openhuman/memory/tree/store_tests.rs b/src/openhuman/memory/tree/store_tests.rs
index cb70b7dda..ff77d4364 100644
--- a/src/openhuman/memory/tree/store_tests.rs
+++ b/src/openhuman/memory/tree/store_tests.rs
@@ -101,7 +101,26 @@ fn chunk_embeddings_are_scoped_by_model_signature() {
             .unwrap()
             .is_none()
     );
+
+    // #1574 cutover: the public `get_chunk_embedding` now reads the sidecar at
+    // the *active* signature (not the legacy column). Nothing was written
+    // there yet, so it is absent — graceful, never a cross-space read of the
+    // openai/local rows above.
     assert!(get_chunk_embedding(&cfg, &c.id).unwrap().is_none());
+
+    // The public setter targets the active signature and round-trips through
+    // the public getter — proves the cutover wiring end to end.
+    set_chunk_embedding(&cfg, &c.id, &[0.7, 0.8]).unwrap();
+    assert_eq!(
+        get_chunk_embedding(&cfg, &c.id).unwrap(),
+        Some(vec![0.7, 0.8])
+    );
+
+    // ...and the earlier per-signature rows remain independently scoped.
+    assert_eq!(
+        get_chunk_embedding_for_signature(&cfg, &c.id, "local/bge-small@384").unwrap(),
+        Some(vec![0.3, 0.4, 0.5])
+    );
 }
 
 #[test]
@@ -236,3 +255,88 @@ fn schema_has_content_path_and_content_sha256_columns() {
     })
     .unwrap();
 }
+
+/// #1574 §7: the one-shot, version-gated legacy→sidecar migration copies a
+/// legacy `embedding` blob whose dimensionality matches the active embedder
+/// into the per-model sidecar at the active signature, skips dim-mismatched
+/// rows (left for the §6 re-embed), keeps the legacy column, and runs exactly
+/// once (PRAGMA user_version gate).
+#[test]
+fn legacy_embeddings_migrate_to_sidecar_once() {
+    let (_tmp, cfg) = test_config();
+    let c_match = sample_chunk("slack:#eng", 0, 1_700_000_000_000);
+    let c_mismatch = sample_chunk("slack:#eng", 1, 1_700_000_000_001);
+    // First open runs the (no-op) migration and sets user_version = 1.
+    upsert_chunks(&cfg, &[c_match.clone(), c_mismatch.clone()]).unwrap();
+
+    // Resolve the active signature/dims exactly as the migration does —
+    // base-independent, never hard-coded (see the brittle-literal lesson).
+    let (p, m, dims) = crate::openhuman::memory::store::effective_embedding_settings(
+        &cfg.memory,
+        cfg.workload_local_model("embeddings").as_deref(),
+    );
+    let sig = crate::openhuman::embeddings::format_embedding_signature(&p, &m, dims);
+    let match_vec = vec![0.25f32; dims];
+    let mismatch_vec = vec![0.5f32; dims + 1];
+
+    // Simulate a pre-#1574 DB: legacy columns populated, migration not yet
+    // run. On entry user_version is 1 (from upsert above) so the migration
+    // is skipped here; the closure then resets the gate to 0.
+    with_connection(&cfg, |conn| {
+        conn.execute(
+            "UPDATE mem_tree_chunks SET embedding = ?1 WHERE id = ?2",
+            params![embedding_to_blob(&match_vec), c_match.id],
+        )?;
+        conn.execute(
+            "UPDATE mem_tree_chunks SET embedding = ?1 WHERE id = ?2",
+            params![embedding_to_blob(&mismatch_vec), c_mismatch.id],
+        )?;
+        conn.pragma_update(None, "user_version", 0i64)?;
+        Ok(())
+    })
+    .unwrap();
+
+    // The next store open (this getter's `with_connection`) sees
+    // user_version = 0 and runs the migration before returning.
+    assert_eq!(
+        get_chunk_embedding_for_signature(&cfg, &c_match.id, &sig).unwrap(),
+        Some(match_vec.clone()),
+        "matching-dim legacy row must be copied to the sidecar at the active sig"
+    );
+    assert!(
+        get_chunk_embedding_for_signature(&cfg, &c_mismatch.id, &sig)
+            .unwrap()
+            .is_none(),
+        "dim-mismatched legacy row must be skipped (left for §6 re-embed)"
+    );
+
+    with_connection(&cfg, |conn| {
+        let legacy: Option<Vec<u8>> = conn
+            .query_row(
+                "SELECT embedding FROM mem_tree_chunks WHERE id = ?1",
+                params![c_match.id],
+                |r| r.get(0),
+            )
+            .unwrap();
+        assert!(
+            legacy.is_some(),
+            "legacy column must be KEPT post-migration (vN+1 drops it later)"
+        );
+        let v: i64 = conn
+            .query_row("PRAGMA user_version", [], |r| r.get(0))
+            .unwrap();
+        assert_eq!(
+            v, TREE_EMBEDDING_MIGRATION_VERSION,
+            "version gate must be set"
+        );
+        Ok(())
+    })
+    .unwrap();
+
+    // Idempotent: subsequent opens are no-ops (gate set); sidecar unchanged.
+    with_connection(&cfg, |_| Ok(())).unwrap();
+    assert_eq!(
+        get_chunk_embedding_for_signature(&cfg, &c_match.id, &sig).unwrap(),
+        Some(match_vec)
+    );
+}
diff --git a/src/openhuman/memory/tree/tree_global/digest.rs b/src/openhuman/memory/tree/tree_global/digest.rs
index 87e3cde77..36c8666d5 100644
--- a/src/openhuman/memory/tree/tree_global/digest.rs
+++ b/src/openhuman/memory/tree/tree_global/digest.rs
@@ -247,7 +247,12 @@ pub async fn end_of_day_digest(
     let tree_id_clone = global.id.clone();
     with_connection(config, move |conn| {
         let tx = conn.unchecked_transaction()?;
-        store::insert_summary_tx(&tx, &daily_clone, Some(&staged_daily))?;
+        store::insert_summary_tx(
+            &tx,
+            &daily_clone,
+            Some(&staged_daily),
+            &crate::openhuman::memory::tree::store::tree_active_signature(config),
+        )?;
         // Index any entities the summariser emitted (no-op under inert).
         crate::openhuman::memory::tree::score::store::index_summary_entity_ids_tx(
             &tx,
diff --git a/src/openhuman/memory/tree/tree_global/seal.rs b/src/openhuman/memory/tree/tree_global/seal.rs
index 6cbe3738e..4364d10b1 100644
--- a/src/openhuman/memory/tree/tree_global/seal.rs
+++ b/src/openhuman/memory/tree/tree_global/seal.rs
@@ -307,7 +307,12 @@ async fn seal_one_level(
             .map(|n| n.max(0) as u32)
             .context("Failed to read current max_level for global tree")?;
 
-        store::insert_summary_tx(&tx, &node, Some(&staged_global))?;
+        store::insert_summary_tx(
+            &tx,
+            &node,
+            Some(&staged_global),
+            &crate::openhuman::memory::tree::store::tree_active_signature(config),
+        )?;
         // Index any entities the summariser emitted. No-op under
         // InertSummariser (entities stays empty by design — see
         // summariser/inert.rs). Becomes active when the Ollama summariser
@@ -452,7 +457,12 @@ mod tests {
     fn insert_daily(cfg: &Config, node: &SummaryNode) {
         with_connection(cfg, |conn| {
             let tx = conn.unchecked_transaction()?;
-            store::insert_summary_tx(&tx, node, None)?;
+            store::insert_summary_tx(
+                &tx,
+                node,
+                None,
+                &crate::openhuman::memory::tree::store::tree_active_signature(cfg),
+            )?;
             tx.commit()?;
             Ok(())
         })
diff --git a/src/openhuman/memory/tree/tree_source/bucket_seal.rs b/src/openhuman/memory/tree/tree_source/bucket_seal.rs
index 9289fd0a5..e0a96526f 100644
--- a/src/openhuman/memory/tree/tree_source/bucket_seal.rs
+++ b/src/openhuman/memory/tree/tree_source/bucket_seal.rs
@@ -629,7 +629,12 @@ pub(crate) async fn seal_one_level(
             .map(|n| n.max(0) as u32)
             .context("Failed to read current max_level for tree")?;
 
-        store::insert_summary_tx(&tx, &node, Some(&staged))?;
+        store::insert_summary_tx(
+            &tx,
+            &node,
+            Some(&staged),
+            &crate::openhuman::memory::tree::store::tree_active_signature(config),
+        )?;
         // Forward-compat: index any entities the summariser emitted into
         // `mem_tree_entity_index` so Phase 4 retrieval can resolve
         // "summaries mentioning Alice" via the same inverted index as
diff --git a/src/openhuman/memory/tree/tree_source/store.rs b/src/openhuman/memory/tree/tree_source/store.rs
index 2ecd8721f..41a572519 100644
--- a/src/openhuman/memory/tree/tree_source/store.rs
+++ b/src/openhuman/memory/tree/tree_source/store.rs
@@ -190,14 +190,18 @@ pub(crate) fn insert_summary_tx(
     tx: &Transaction<'_>,
     node: &SummaryNode,
     staged: Option<&StagedSummary>,
+    model_signature: &str,
 ) -> Result<()> {
-    let embedding_blob: Option<Vec<u8>> = match node.embedding.as_deref() {
-        Some(v) => Some(
-            pack_checked(v)
-                .with_context(|| format!("Failed to pack embedding for summary id={}", node.id))?,
-        ),
-        None => None,
-    };
+    // #1574 write-side cutover: keep the dimension guard (fail the seal fast
+    // on a misconfigured embedder) but DO NOT write the legacy
+    // `mem_tree_summaries.embedding` column — the vector is persisted to the
+    // per-model sidecar below, in THIS tx so it commits atomically with the
+    // summary row. The legacy column is left NULL for the §7 migration.
+    if let Some(v) = node.embedding.as_deref() {
+        pack_checked(v)
+            .with_context(|| format!("validate embedding dims for summary id={}", node.id))?;
+    }
+    let embedding_blob: Option<Vec<u8>> = None;
 
     // Phase MD-content: when a staged file exists, truncate `content` to a
     // ≤500-char plain-text preview (char boundary safe via chars().take(500)).
@@ -244,59 +248,60 @@ pub(crate) fn insert_summary_tx(
         ],
     )
     .with_context(|| format!("Failed to insert summary id={}", node.id))?;
+
+    // #1574: persist the embedding to the per-model sidecar at the active
+    // signature, in the SAME tx as the summary row insert above.
+    if let Some(v) = node.embedding.as_deref() {
+        upsert_summary_embedding_conn(tx, &node.id, model_signature, v)?;
+    }
     Ok(())
 }
 
 /// Set (or overwrite) the embedding for an existing summary row.
-/// Exposed for a future backfill helper — not called by ingest/seal
-/// today. Returns the number of rows updated (0 if the id is unknown).
+///
+/// #1574 cutover: writes the per-model `mem_tree_summary_embeddings` sidecar
+/// at the active signature (via [`set_summary_embedding_for_signature`])
+/// instead of the legacy `mem_tree_summaries.embedding` column. The signature
+/// is resolved internally from `config` via the shared
+/// [`crate::openhuman::memory::tree::store::tree_active_signature`] — same
+/// resolution as the chunk path. Returns `1` on success (one sidecar row
+/// written/updated); the legacy "0 if id unknown" count no longer applies
+/// since the sidecar upsert does not join the parent summary row.
 pub fn set_summary_embedding(
     config: &Config,
     summary_id: &str,
     embedding: &[f32],
 ) -> Result<usize> {
-    let blob = pack_checked(embedding)
-        .with_context(|| format!("Failed to pack embedding for summary id={summary_id}"))?;
-    with_connection(config, |conn| {
-        let changed = conn.execute(
-            "UPDATE mem_tree_summaries SET embedding = ?1 WHERE id = ?2",
-            params![blob, summary_id],
-        )?;
-        if changed == 0 {
-            log::warn!(
-                "[tree_source::store] set_summary_embedding: no row for summary_id={summary_id}"
-            );
-        }
-        Ok(changed)
-    })
+    let signature = crate::openhuman::memory::tree::store::tree_active_signature(config);
+    log::debug!(
+        "[tree_source::store] set_summary_embedding: summary_id={summary_id} sig={signature} dims={}",
+        embedding.len()
+    );
+    set_summary_embedding_for_signature(config, summary_id, &signature, embedding)?;
+    Ok(1)
 }
 
-/// Fetch a summary's embedding, decoding the stored little-endian `f32`
-/// blob. Returns `Ok(None)` if the summary doesn't exist OR if it exists
-/// but has a NULL embedding (legacy / pre-Phase-4 rows).
-pub fn get_summary_embedding(config: &Config, summary_id: &str) -> Result<Option<Vec<f32>>> {
-    with_connection(config, |conn| {
-        let blob: Option<Option<Vec<u8>>> = conn
-            .query_row(
-                "SELECT embedding FROM mem_tree_summaries WHERE id = ?1",
-                params![summary_id],
-                |r| r.get::<_, Option<Vec<u8>>>(0),
-            )
-            .optional()?;
-        match blob {
-            None => Ok(None),
-            Some(inner) => decode_optional_blob(inner, &format!("summary_id={summary_id}")),
-        }
-    })
-}
-
-/// Store a summary embedding for a specific provider/model/dimension signature.
+/// Fetch a summary's embedding for the active model signature.
 ///
-/// This writes the #1574 per-model table only; the legacy
-/// `mem_tree_summaries.embedding` column remains available for dual-read
-/// fallback while query paths migrate.
-pub fn set_summary_embedding_for_signature(
-    config: &Config,
+/// #1574 cutover: reads the per-model `mem_tree_summary_embeddings` sidecar at
+/// the active signature (via [`get_summary_embedding_for_signature`]) instead
+/// of the legacy `mem_tree_summaries.embedding` column. `Ok(None)` when no
+/// vector exists under the active signature — graceful absence during the §7
+/// backfill window, never a cross-space read.
+pub fn get_summary_embedding(config: &Config, summary_id: &str) -> Result<Option<Vec<f32>>> {
+    let signature = crate::openhuman::memory::tree::store::tree_active_signature(config);
+    get_summary_embedding_for_signature(config, summary_id, &signature)
+}
+
+/// Core upsert into `mem_tree_summary_embeddings` over an arbitrary
+/// `&Connection`. Shared by the standalone
+/// ([`set_summary_embedding_for_signature`]) and in-transaction
+/// ([`set_summary_embedding_for_signature_tx`]) write paths so the SQL exists
+/// exactly once. `rusqlite::Transaction` derefs to `Connection`, so the seal
+/// path passes `&tx` and the sidecar row commits atomically with the summary
+/// row insert (#1574 write-side cutover).
+fn upsert_summary_embedding_conn(
+    conn: &rusqlite::Connection,
     summary_id: &str,
     model_signature: &str,
     embedding: &[f32],
@@ -304,21 +309,48 @@ pub fn set_summary_embedding_for_signature(
     let blob = pack_embedding_blob(embedding);
     let dim = i64::try_from(embedding.len()).context("embedding dimension does not fit i64")?;
     let created_at = Utc::now().timestamp_millis() as f64 / 1000.0;
-    with_connection(config, |conn| {
-        conn.execute(
-            "INSERT INTO mem_tree_summary_embeddings
+    conn.execute(
+        "INSERT INTO mem_tree_summary_embeddings
              (summary_id, model_signature, vector, dim, created_at)
              VALUES (?1, ?2, ?3, ?4, ?5)
              ON CONFLICT(summary_id, model_signature) DO UPDATE SET
                 vector = excluded.vector,
                 dim = excluded.dim,
                 created_at = excluded.created_at",
-            params![summary_id, model_signature, blob, dim, created_at],
-        )?;
-        Ok(())
+        params![summary_id, model_signature, blob, dim, created_at],
+    )?;
+    Ok(())
+}
+
+/// Store a summary embedding for a specific provider/model/dimension signature.
+///
+/// Per-model table write path for #1574. The legacy
+/// `mem_tree_summaries.embedding` column is intentionally left untouched by
+/// this helper (read by the §7 migration; dropped only in a later release).
+pub fn set_summary_embedding_for_signature(
+    config: &Config,
+    summary_id: &str,
+    model_signature: &str,
+    embedding: &[f32],
+) -> Result<()> {
+    with_connection(config, |conn| {
+        upsert_summary_embedding_conn(conn, summary_id, model_signature, embedding)
     })
 }
 
+/// Transaction-scoped variant of [`set_summary_embedding_for_signature`], for
+/// the seal path which inserts the summary row and its embedding in one tx
+/// (#1574 write-side cutover). Opening a fresh connection there would break
+/// atomicity / deadlock on the busy DB.
+pub(crate) fn set_summary_embedding_for_signature_tx(
+    tx: &rusqlite::Transaction<'_>,
+    summary_id: &str,
+    model_signature: &str,
+    embedding: &[f32],
+) -> Result<()> {
+    upsert_summary_embedding_conn(tx, summary_id, model_signature, embedding)
+}
+
 /// Fetch a summary embedding for exactly one provider/model/dimension signature.
 pub fn get_summary_embedding_for_signature(
     config: &Config,
diff --git a/src/openhuman/memory/tree/tree_source/store_tests.rs b/src/openhuman/memory/tree/tree_source/store_tests.rs
index 9ec665a1b..9570e9364 100644
--- a/src/openhuman/memory/tree/tree_source/store_tests.rs
+++ b/src/openhuman/memory/tree/tree_source/store_tests.rs
@@ -74,7 +74,7 @@ fn summary_insert_and_fetch() {
     let node = sample_summary("sum-1", "tree-1", 1);
     with_connection(&cfg, |conn| {
         let tx = conn.unchecked_transaction()?;
-        insert_summary_tx(&tx, &node, None)?;
+        insert_summary_tx(&tx, &node, None, "test")?;
         tx.commit()?;
         Ok(())
     })
@@ -93,8 +93,8 @@ fn summary_insert_is_idempotent_on_id() {
     let node = sample_summary("sum-1", "tree-1", 1);
     with_connection(&cfg, |conn| {
         let tx = conn.unchecked_transaction()?;
-        insert_summary_tx(&tx, &node, None)?;
-        insert_summary_tx(&tx, &node, None)?;
+        insert_summary_tx(&tx, &node, None, "test")?;
+        insert_summary_tx(&tx, &node, None, "test")?;
         tx.commit()?;
         Ok(())
     })
@@ -109,7 +109,7 @@ fn summary_embeddings_are_scoped_by_model_signature() {
     let node = sample_summary("sum-embed", "tree-1", 1);
     with_connection(&cfg, |conn| {
         let tx = conn.unchecked_transaction()?;
-        insert_summary_tx(&tx, &node, None)?;
+        insert_summary_tx(&tx, &node, None, "test")?;
         tx.commit()?;
         Ok(())
     })
@@ -143,7 +143,25 @@ fn summary_embeddings_are_scoped_by_model_signature() {
             .unwrap()
             .is_none()
     );
+
+    // #1574 cutover: the public `get_summary_embedding` now reads the sidecar
+    // at the *active* signature (not the legacy column). Nothing is written
+    // there yet → absent; never a cross-space read of the rows above.
     assert!(get_summary_embedding(&cfg, "sum-embed").unwrap().is_none());
+
+    // The public setter targets the active signature and round-trips through
+    // the public getter — proves the cutover wiring end to end.
+    set_summary_embedding(&cfg, "sum-embed", &[0.7, 0.8]).unwrap();
+    assert_eq!(
+        get_summary_embedding(&cfg, "sum-embed").unwrap(),
+        Some(vec![0.7, 0.8])
+    );
+
+    // ...and the earlier per-signature rows remain independently scoped.
+    assert_eq!(
+        get_summary_embedding_for_signature(&cfg, "sum-embed", "local/bge-small@384").unwrap(),
+        Some(vec![0.3, 0.4, 0.5])
+    );
 }
 
 #[test]
diff --git a/tests/linux_cef_deb_runtime_e2e.rs b/tests/linux_cef_deb_runtime_e2e.rs
index baf6c8aa7..2ef1ddd87 100644
--- a/tests/linux_cef_deb_runtime_e2e.rs
+++ b/tests/linux_cef_deb_runtime_e2e.rs
@@ -12,24 +12,47 @@
 use std::fs;
 use std::io::Write;
 use std::path::PathBuf;
+use std::sync::{Mutex, MutexGuard};
 
-/// Guard to temporarily set/unset environment variables.
+/// Serializes every env-mutating test in this file. `std::env` is
+/// process-global; cargo runs these tests in parallel within one binary,
+/// and several mutate the SAME vars (e.g. `OPENHUMAN_CORE_BIN`), so without
+/// this an interleaving made one test read back another's value and the
+/// `assert_eq!` flaked. `EnvGuard` holds this lock for its whole lifetime,
+/// so at most one env-mutating test runs at a time. Poison-safe (a
+/// panicking test must not cascade-fail every later one).
+static ENV_LOCK: Mutex<()> = Mutex::new(());
+
+/// Guard to temporarily set/unset environment variables. Acquires
+/// [`ENV_LOCK`] for its lifetime so concurrent tests can't observe each
+/// other's mutations.
 struct EnvGuard {
     key: &'static str,
     old: Option<String>,
+    _lock: MutexGuard<'static, ()>,
 }
 
 impl EnvGuard {
     fn set(key: &'static str, value: &str) -> Self {
+        let lock = ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
         let old = std::env::var(key).ok();
         std::env::set_var(key, value);
-        Self { key, old }
+        Self {
+            key,
+            old,
+            _lock: lock,
+        }
     }
 
     fn unset(key: &'static str) -> Self {
+        let lock = ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
         let old = std::env::var(key).ok();
         std::env::remove_var(key);
-        Self { key, old }
+        Self {
+            key,
+            old,
+            _lock: lock,
+        }
     }
 }