fix(postinstall): cross-platform node shim instead of POSIX shell (#1554)

* fix(postinstall): cross-platform node shim instead of POSIX shell

The postinstall script used POSIX shell syntax ('command -v',
'>/dev/null 2>&1', '1>&2') which Bun's built-in script parser rejects
on Windows. 'bun install' aborted with 'expected a command or
assignment but got: "Redirect"' before gbrain could ever be probed.

Replace with a one-liner 'node -e' shim that:

* uses spawnSync to probe 'gbrain --version' (shell:true on win32 so
  the Windows shim/.cmd resolution works)
* on success: runs 'gbrain apply-migrations --yes --non-interactive'
  and propagates its exit code
* on failure: writes the same skip message to stderr and exits 0, so
  fresh clones (where gbrain isn't on PATH yet) still complete install

POSIX hosts retain the original behavior; Windows hosts now succeed
instead of failing the whole install.

Fixes #1486

* fix(postinstall): move logic to scripts/postinstall.ts to survive Bun Windows script-runner

The `node -e` inline shim still failed on Windows under Bun. Embedding a
program inside the package.json postinstall string lets the lifecycle shell
mangle it: Bun's Windows script-runner expands the `\n` in the hint string
into a REAL newline before node sees it, producing `SyntaxError: Invalid or
unexpected token` and aborting the whole install. `node` is also not
guaranteed present under a Bun install (bun is the guaranteed runtime), and
`shell: win32` re-opened a quoting surface.

Move the logic into a checked-in `scripts/postinstall.ts` run via
`bun run scripts/postinstall.ts`, matching the repo's existing convention of
~19 scripts under scripts/*.ts. This sidesteps all three failure modes:

* `which('gbrain')` from bun does Windows-aware PATH resolution (finds
  gbrain / gbrain.exe / gbrain.cmd) with no shell.
* `Bun.spawnSync` with an argv array invokes apply-migrations directly —
  no shell, nothing to quote, no `\n` expansion.
* No dependency on `node` being present; bun runs the script.

Behavior is preserved exactly: same `apply-migrations --yes
--non-interactive` command, same issue-218 skip hint, and the same
never-fail-the-install guarantee (every path exits 0). Verified on macOS:
`bun run scripts/postinstall.ts` exits 0 on the skip path (gbrain absent),
on a failing migration, and on a successful migration.

Fixes #1486

package.json

@@ -84,7 +84,7 @@
     "check:fixture-privacy": "scripts/check-fixture-privacy.sh",
     "check:conversation-parser": "bun src/cli.ts eval conversation-parser test/fixtures/conversation-formats/all.jsonl --no-llm",
     "check:source-scope-onboard": "scripts/check-source-scope-onboard.sh",
-    "postinstall": "command -v gbrain >/dev/null 2>&1 && gbrain apply-migrations --yes --non-interactive || echo '[gbrain] postinstall skipped. If installed via bun install -g github:...: run `gbrain doctor` and `gbrain apply-migrations --yes` manually. See https://github.com/garrytan/gbrain/issues/218' 1>&2",
+    "postinstall": "bun run scripts/postinstall.ts",
     "prepublish:clawhub": "bun run build:all",
     "publish:clawhub": "clawhub package publish . --family bundle-plugin"
   },

scripts/postinstall.ts

@@ -0,0 +1,49 @@
+#!/usr/bin/env bun
+// scripts/postinstall.ts
+//
+// Postinstall hook: after `bun install`, apply any pending schema migrations so
+// a freshly-installed gbrain is immediately usable. Wired via package.json
+// ("postinstall": "bun run scripts/postinstall.ts") as a real Bun script rather
+// than an inline `node -e` one-liner.
+//
+// Why a script file and not an inline command:
+//   Embedding a program inside the package.json postinstall string lets the
+//   lifecycle shell mangle it. Bun's Windows script-runner expands `\n` in the
+//   hint string into a REAL newline before node sees it, producing
+//   `SyntaxError: Invalid or unexpected token` and aborting the whole install.
+//   `node` is also not guaranteed present under a Bun install (bun is the
+//   guaranteed runtime), and `shell: win32` re-opens a quoting surface. A
+//   checked-in .ts run by `bun run` sidesteps all three.
+//
+// Uses Bun APIs only — `which()` for Windows-aware PATH resolution (finds
+// gbrain.exe / gbrain.cmd) and an argv-array `Bun.spawnSync` (no shell, nothing
+// to quote). It NEVER fails the install: every path exits 0.
+
+import { which } from 'bun';
+
+const HINT =
+  '[gbrain] postinstall skipped. If installed via bun install -g github:...: ' +
+  'run `gbrain doctor` and `gbrain apply-migrations --yes` manually. ' +
+  'See https://github.com/garrytan/gbrain/issues/218';
+
+// Windows-aware PATH resolution — finds gbrain, gbrain.exe or gbrain.cmd.
+const bin = which('gbrain');
+
+if (!bin) {
+  // Fresh clone / global install where gbrain isn't on PATH yet: skip cleanly.
+  console.error(HINT);
+  process.exit(0);
+}
+
+try {
+  const r = Bun.spawnSync({
+    cmd: [bin, 'apply-migrations', '--yes', '--non-interactive'],
+    stdout: 'inherit',
+    stderr: 'inherit',
+  });
+  if (r.exitCode !== 0) console.error(HINT);
+} catch {
+  console.error(HINT);
+}
+
+process.exit(0); // never abort the install