fix(dream): deterministic last-writer attribution for colliding slugs

collectChildPutPageSlugs paired each slug to a jobId first-seen over an
unordered result set. When two children collide on a final slug, the pages
row holds the LAST put_page write, so the provenance stamp
(transcript_id/transcript_source/date) could attribute an arbitrary other
transcript. ORDER BY id + last-writer-wins aligns the stamp with the
surviving content; pinned by a collision test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/core/cycle/synthesize.ts

@@ -1139,7 +1139,8 @@ async function collectChildPutPageSlugs(
        FROM subagent_tool_executions
       WHERE job_id = ANY($1::int[])
         AND tool_name = 'brain_put_page'
-        AND status = 'complete'`,
+        AND status = 'complete'
+      ORDER BY id`,
     [childIds],
   );
   const rewritten = new Map<string, number>();
@@ -1149,7 +1150,10 @@ async function collectChildPutPageSlugs(
     const finalSlug = meta && meta.chunkTotal > 1
       ? rewriteChunkedSlug(r.slug, meta.hash6, meta.idx)
       : r.slug;
-    if (!rewritten.has(finalSlug)) rewritten.set(finalSlug, r.job_id);
+    // Last writer wins, in execution-row order (ORDER BY id): if two children
+    // collide on a final slug, the pages row holds the LAST put_page write, so
+    // the stamp must attribute that child's transcript — not an arbitrary one.
+    rewritten.set(finalSlug, r.job_id);
   }
   return [...rewritten.entries()]
     .sort(([a], [b]) => a.localeCompare(b))

test/cycle-synthesize-slug-collection.test.ts

@@ -174,6 +174,25 @@ describe('#2285: orchestrator-owned deterministic transcript frontmatter', () =>
     }
   });
 
+  test('slug collision across children attributes the LAST writer (matches surviving putPage)', async () => {
+    const db = (engine as any).db;
+    // Jobs 1001 then 1002 write the same slug; the pages row would hold
+    // 1002's content (last put_page wins), so the ref must carry jobId 1002.
+    await db.query(
+      `INSERT INTO subagent_tool_executions (job_id, message_idx, tool_use_id, tool_name, status, input)
+       VALUES (1001, 9, 'tool_dup_a', 'brain_put_page', 'complete', $1::jsonb)`,
+      [JSON.stringify({ slug: 'wiki/agents/test/collision', body: 'first' })],
+    );
+    await db.query(
+      `INSERT INTO subagent_tool_executions (job_id, message_idx, tool_use_id, tool_name, status, input)
+       VALUES (1002, 9, 'tool_dup_b', 'brain_put_page', 'complete', $1::jsonb)`,
+      [JSON.stringify({ slug: 'wiki/agents/test/collision', body: 'second' })],
+    );
+    const refs = await collectChildPutPageSlugs(engine as any, [1001, 1002], new Map());
+    const hit = refs.find((r: { slug: string }) => r.slug === 'wiki/agents/test/collision');
+    expect(hit?.jobId).toBe(1002);
+  });
+
   test('stampDreamProvenance merges the transcript metadata into DB frontmatter', async () => {
     const slug = 'wiki/originals/ideas/2026-07-17-transcript-meta-abc123';
     await engine.putPage(slug, {