refactor(code-index): extract single-file preparation

[WebMad]

Summary

• Extract single-file exclusions, size/read, hash comparison, parsing, optional embedding and point construction into FilePreparation, with explicit constructor injection and an instance prepareFile() method.
• Define the narrowly typed FilePreparationDependencies interface in its own file. Inject the original service objects through narrow contracts: Pick<CacheManager, "getHash">, Pick<RooIgnoreController, "validateAccess">, and Pick<FileSystem, "stat" | "readFile">. No callback adapters or wrapper classes; URI conversion happens inside preparation at the IO boundary.
• Each FileWatcher constructs one readonly preparation instance in its constructor. Public processFile() delegates to that reused instance; existing factories and consumers are unchanged.
• Preparation only looks up cached hashes and returns the existing result type: it cannot write points, mutate the cache, or own watchers/timers.

Scope and preserved behavior

The extraction preserves exclusion order and reasons, size boundary, optional embedder, empty points plus new hash, normalized paths, UUID generation, embedding order, and original error values. This PR now also includes one explicit UTF-8 contract fix; it is no longer strictly behavior-preserving.

At the read boundary, decode with Buffer.from(fileContent).toString("utf-8"), matching scanner semantics. Plain byte arrays must produce text rather than comma-separated decimal byte values. Preserve UTF-8 BOM as U+FEFF and lossy U+FFFD replacement for invalid sequences; hash the decoded string with SHA-256, not the raw bytes, consistent with the parser. Respect sliced-view byte offset and length. Constructor-injected service objects and the existing method decomposition remain unchanged.

No encoding detection, UTF-16 support, BOM stripping, editor-document decoding, new helper, or raw-byte hashing is introduced. This does not claim to solve all encoding issues.

No fixes to deletion ordering, empty-result hash persistence, batch concurrency, restart/session ownership, or drain behavior. Independent branch from fetched upstream main at d351a15; does not include PR #1835 restart changes. Existing PRs remain untouched.

Tests and validation

• Preparation suite: 66 tests passed, explicitly exercising POSIX and Windows path semantics.
• UTF-8 matrix: both buffer representations cover ASCII, Cyrillic/Spanish/CJK/emoji, preserved BOM, empty input, invalid/truncated UTF-8, and a sliced view with nonzero byte offset. Literal expected text (including U+FEFF/U+FFFD) drives expected hashes. Each case checks parser content/hash, returned hash, and unchanged-cache skip.
• Red before fix: replacing the incorrect decimal-string expectation with AB produced 2 failed / 42 passed, with the intended content/hash mismatch in both path modes. The one-line production fix then gave 44/44 passed, before expanding the matrix.
• Targeted preparation/watcher/processor-factory suites: 80 tests passed in 3 files.
• Full code-index suite: 747 tests passed in 31 files (baseline 725; net +22).
• Full backend services directory: 1750 tests passed, 13 skipped; 129 files passed, 2 skipped (baseline 1728; net +22).
• Dedicated services configuration additionally passed: 1285 tests passed, 1 skipped in 66 files.
• Backend TypeScript and changed-file ESLint with suppression pruning passed; the suppression file remains unchanged after formatting, so counts did not increase.
• Commit/push hooks were enabled and passed: staged formatting, repository lint and repository typechecks.
• Validation ran locally on macOS with explicit POSIX/Windows path semantics. Native Windows execution is left to CI; no native Windows success is claimed here.

Environment caveat: local Node 24.7.0 differs from the required 22.23.1, producing the existing engine warning. Prettier reports the existing unknown ignore-option warning. An initial full-suite invocation used an unsupported Vitest reporter and failed before tests started; the standard-reporter rerun passed. No changesets, changelogs, or local split-plan file are included in the fix.

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src/services/code-index/processors/file-preparation.ts (1)

23-23: LGTM!

src/services/code-index/processors/__tests__/file-preparation.spec.ts (1)

213-226: LGTM!

Also applies to: 238-293

---

📝 Summary

Summary by CodeRabbit

• Code Indexing
  • Files that are ignored, inaccessible, too large, or unchanged are skipped.
  • Eligible files are parsed and, when embeddings are available, prepared for indexing. Processing errors are reported as local errors.
  • Prepared results include a content hash and indexing points when parsing and embedding produce results.
• Quality
  • Expanded test coverage for file preparation, path handling, UTF-8 decoding, filtering, caching, errors, and file-watcher behavior.

Walkthrough

File preparation moves from FileWatcher into a dedicated FilePreparation class. The class checks files, reads and hashes content, parses changed files, creates embedding points when an embedder is available, and returns processing results. FileWatcher delegates processFile to this class.

Changes

File preparation flow

Layer / File(s)	Summary
Prepare files for batching src/services/code-index/processors/file-preparation-dependencies.ts, src/services/code-index/processors/file-preparation.ts, src/services/code-index/processors/__tests__/file-preparation.spec.ts	FilePreparation checks access, ignore rules, file size, and cached hashes before processing content. It returns generated points and the new hash for batching, or a skipped or local-error result. Tests cover POSIX and Windows paths, UTF-8 decoding, size limits, unchanged content, point IDs, embeddings, receiver preservation, and error propagation.
Delegate watcher processing src/services/code-index/processors/file-watcher.ts, src/services/code-index/processors/__tests__/file-watcher.spec.ts	FileWatcher constructs FilePreparation with its processing dependencies and delegates processFile to it. A test checks instance reuse, returned results, workspace reads, and the absence of direct point or cache writes.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to 4f2d5

The file-preparation extraction has no identified merge-blocking issue. Merge after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 4f2d5

The watcher still coordinates indexing, and the extracted preparation method checks ignore rules, access, and file size before reading content. No new security exposure was established, but caller and recovery coverage is not exhaustive.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The effective path evidenced here remains workspace-file preparation through FileWatcher, with prepared code chunks reaching the watcher’s vector upsert path. A separate production caller of the new public method was not established by the available caller evidence.

Trust Boundaries and Controls

• observed — The extracted entrypoint retains file-admission checks before content access; a caller using prepareFile does not bypass those checks merely by bypassing FileWatcher.processFile.

Resilience and Maintainability Implications

• observed — Preparation converts stage failures to local-error results. The watcher handles those results separately from prepared points and retries failed vector upserts before advancing hashes.

🚥 Pre-merge checks | ✅ 7 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description provides detailed implementation, scope, behavior, and test information. However, it omits the required approved GitHub Issue link and does not include the required template sections o…	Add the Related GitHub Issue section with an issue number, use the required Description and Test Procedure headings, and complete the Pre-Submission Checklist. Preserve the existing implementation and validation details.

✅ Passed checks (7 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Regression Evidence	✅ Passed	PASS — Focused tests cover the extracted FilePreparation behavior at the lowest valid layer. Coverage includes exclusion order, access and ignore branches, size boundaries, cached hashes, empty and po…
Security Boundaries	✅ Passed	No changed path meets the failure condition. FilePreparation.prepareFile() performs the existing ignored-directory, validateAccess, and ignore-instance checks before stat and readFile. The wat…
Persistence Integrity	✅ Passed	No changed persistence path meets the failure condition. FilePreparation.prepareFile() only reads the cached hash through getHash() and returns newHash; it does not write points or update the ca…
Lifecycle Resource Cleanup	✅ Passed	No changed lifecycle path introduces a resource leak or duplicate work. The PR adds FilePreparation, which stores injected service references but creates no listener, watcher, timer, provider, or pe…
Title check	✅ Passed	The title clearly and concisely describes the primary change: extracting single-file preparation from FileWatcher.

Full details: Description check

Explanation

The description provides detailed implementation, scope, behavior, and test information. However, it omits the required approved GitHub Issue link and does not include the required template sections or completed pre-submission checklist.

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Actionable comments posted: 1

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Inline comments:
Review comments at
@src/services/code-index/processors/__tests__/file-preparation.spec.ts:
- Line 214: Update the receiver assertions in the file-preparation test to
verify object identity: assert each relevant `mock.contexts[0]` with `.toBe()`
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Check persistence and lifecycle invariants: awaited atomic writes, rollback or explicit partial-failure behavior, cross-window state consistency, stale listeners/watchers, cancellation, idempotency, and safe restart/resume without lost or d...

⚙️ CodeRabbit configuration file

Files:

• src/services/code-index/processors/__tests__/file-preparation.spec.ts
• src/services/code-index/processors/file-preparation.ts

Require regression coverage at the lowest valid harness with behavior-focused assertions, including relevant negative, error, false/unset, and boundary cases.

⚙️ CodeRabbit configuration file

Files:

• src/services/code-index/processors/__tests__/file-preparation.spec.ts

Check strict typing and exhaustive behavior across normal, boundary, error, cancellation, retry, and compatibility paths.

⚙️ CodeRabbit configuration file

Files:

• src/services/code-index/processors/__tests__/file-preparation.spec.ts
• src/services/code-index/processors/file-preparation.ts

Verify extension/webview contracts, cancellation and error propagation, VS Code lifecycle correctness, and behavior under retries and partial failure.

⚙️ CodeRabbit configuration file

Files:

• src/services/code-index/processors/__tests__/file-preparation.spec.ts
• src/services/code-index/processors/file-preparation.ts

Act as an adversarial second-opinion reviewer.

⚙️ CodeRabbit configuration file

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• src/services/code-index/processors/__tests__/file-preparation.spec.ts
• src/services/code-index/processors/file-preparation.ts

🔇 Additional comments (1)

src/services/code-index/processors/file-preparation.ts (1)

17-19: LGTM!

Also applies to: 27-27, 31-31, 35-35, 42-42, 48-99