fix: sync update-graph.sh hook extension allowlist with EXTENSIONS

[carlos-alm]

Summary

• .claude/hooks/update-graph.sh's PostToolUse hook only rebuilt the graph for a hardcoded extension allowlist that was missing .mjs/.cjs (both registered JS extensions), silently going stale after edits to those files.
• Fixed via a build-time generated artifact (dist/hook-extensions.txt, produced from EXTENSIONS by scripts/gen-hook-extensions.mjs) read with native grep -qxF — measured ~10ms overhead vs. dynamically importing EXTENSIONS at runtime, which would add 30-60ms to every single edit (transitively pulls in web-tree-sitter). Kept a fully-synced hardcoded case fallback for environments without a local dist/ build, protected by a new drift test.

Closes #1736

Test plan

• npm test — full suite green (3434 passed, 0 failed)
• npm run lint — clean
• New drift test verified to actually catch drift (temporarily stripped extensions from the fallback list, confirmed precise failure message, restored)
• Traced hook execution end-to-end for .mjs/.md/.cjs(artifact removed)/.txt(artifact removed) — all four behave correctly

Filed #1836 for an out-of-scope finding: the hook's rarely-used fallback build path references a nonexistent src/cli.js (should be dist/cli.js).

Stacked on #1835 (base branch fix/issue-1734-communities-drift-nondeterminism) — only the hooks/scripts/test diff is this issue's change.

[greptile-apps]

Greptile Summary

This PR fixes a silent staleness bug where .mjs and .cjs files edited in the repo never triggered a codegraph rebuild because the PostToolUse hook's hardcoded extension list was missing those two extensions. The fix replaces the hand-maintained list with a build-time generated artifact (dist/hook-extensions.txt) derived directly from the EXTENSIONS constant, keeping the old case statement only as a pre-build fallback, guarded by a new drift test.

• update-graph.sh: PROJECT_DIR is now resolved before the extension check so it can locate dist/hook-extensions.txt; the primary path uses grep -qxF against the generated file, and the hardcoded case block serves only as a fallback for fresh clones before the first build.
• scripts/gen-hook-extensions.mjs: New build-time script appended to npm run build that reads EXTENSIONS from the compiled output and writes one extension per line, making the hook's primary list automatically stay in sync with LANGUAGE_REGISTRY.
• tests/unit/hook-extensions.test.ts: New drift-guard test that parses the fallback case list and diffs it against EXTENSIONS bidirectionally, plus a conditional test (skipped without a build) that re-runs the generator and validates the output file.

Confidence Score: 5/5

Safe to merge — the hook works correctly in all three environments (artifact present, pre-build fallback, no DB), and the drift test prevents the exact class of silent regression this PR fixes.

The extension-check logic is correct end-to-end: || exit 0 properly handles grep returning 1 under set -euo pipefail, the leading-dot format is consistent between the generator and the hook's EXT computation, and the fallback case list is now kept honest by the drift test.

No files require special attention.

Important Files Changed

Filename	Overview
.claude/hooks/update-graph.sh	Replaces the stale hardcoded case extension list with a grep -qxF check against dist/hook-extensions.txt; the old case block becomes a fallback for pre-build environments. Logic is correct: the `
scripts/gen-hook-extensions.mjs	New build-time script that reads EXTENSIONS from the compiled dist/shared/constants.js and writes one extension per line to dist/hook-extensions.txt. Correctly runs after tsc in the build chain.
tests/unit/hook-extensions.test.ts	New drift-guard test comparing the fallback case list against EXTENSIONS bidirectionally. Previously flagged concerns about the regex character class and comment-vs-functional assertions are addressed in the current code.
package.json	Appends && node scripts/gen-hook-extensions.mjs to the build script, ensuring the extension snapshot is regenerated after every tsc run.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["PostToolUse fires (Edit/Write)"] --> B["Parse FILE_PATH from stdin (Node)"]
    B --> C{"FILE_PATH empty?"}
    C -- Yes --> EXIT0["exit 0"]
    C -- No --> D["EXT = .extension"]
    D --> E{"dist/hook-extensions.txt exists?"}
    E -- Yes --> F["grep -qxF EXT hook-extensions.txt"]
    F -- "not found" --> EXIT0
    F -- "found" --> G
    E -- No --> H["case fallback allowlist"]
    H -- "no match" --> EXIT0
    H -- "match" --> G
    G["Check fixtures path"] --> J{"DB exists?"}
    J -- No --> EXIT0
    J -- Yes --> K{"Marker age > 24h?"}
    K -- Yes --> L["BUILD_FLAGS=--no-incremental"]
    K -- No --> M["BUILD_FLAGS=''"]
    L --> N["Run codegraph build"]
    M --> N
    N --> O{"Full rebuild & succeeded?"}
    O -- Yes --> P["touch last-full-build marker"]
    O -- No --> EXIT0b["exit 0"]
    P --> EXIT0b

    subgraph "npm run build"
        TSC["tsc"] --> COPY["copy index.cjs"] --> GEN["gen-hook-extensions.mjs -> dist/hook-extensions.txt"]
    end

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flowchart TD
    A["PostToolUse fires (Edit/Write)"] --> B["Parse FILE_PATH from stdin (Node)"]
    B --> C{"FILE_PATH empty?"}
    C -- Yes --> EXIT0["exit 0"]
    C -- No --> D["EXT = .extension"]
    D --> E{"dist/hook-extensions.txt exists?"}
    E -- Yes --> F["grep -qxF EXT hook-extensions.txt"]
    F -- "not found" --> EXIT0
    F -- "found" --> G
    E -- No --> H["case fallback allowlist"]
    H -- "no match" --> EXIT0
    H -- "match" --> G
    G["Check fixtures path"] --> J{"DB exists?"}
    J -- No --> EXIT0
    J -- Yes --> K{"Marker age > 24h?"}
    K -- Yes --> L["BUILD_FLAGS=--no-incremental"]
    K -- No --> M["BUILD_FLAGS=''"]
    L --> N["Run codegraph build"]
    M --> N
    N --> O{"Full rebuild & succeeded?"}
    O -- Yes --> P["touch last-full-build marker"]
    O -- No --> EXIT0b["exit 0"]
    P --> EXIT0b

    subgraph "npm run build"
        TSC["tsc"] --> COPY["copy index.cjs"] --> GEN["gen-hook-extensions.mjs -> dist/hook-extensions.txt"]
    end

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_{Reviews (3): Last reviewed commit: "fix: harden hook-extensions regex/assert..." | Re-trigger Greptile}

[carlos-alm]

@greptileai