fix(functions/emulator): hidden-path ignore relative to functionsDir

[kyungseopk1m]

Description

Fixes #10187.

FunctionsEmulator configures chokidar's ignored option with a hidden-segment regex (/(^|[\/\\])\../) that was evaluated against the absolute file path. When the project lives under a dot-prefixed ancestor directory (for example .worktrees/, .cache/, or any other ancestor starting with .), that regex matches the ancestor segment of every path and the watcher silently filters out every change. The result is that saving a source file never triggers a reload.

This change extracts a shouldIgnoreWatchPath(functionsDir, filePath) helper in functionsEmulatorShared.ts that computes path.relative(functionsDir, filePath) and only tests the hidden-segment regex against the relative path. The matcher in functionsEmulator.ts uses that helper in place of the bare regex.

Behavior is preserved for the common case — files like .git/HEAD, .dart_tool/…, or .cache/… inside the watched directory are still ignored, because their relative path starts with a dot. The remaining built-in ignore patterns (.log files, node_modules, venv) and any user-supplied backend.ignore globs are unchanged.

Scenarios Tested

Added unit tests in src/emulator/functionsEmulatorShared.spec.ts covering:

• Hidden file inside the functions directory (.git/HEAD) is still ignored.
• Hidden segment nested within the functions directory (src/.cache/module.js) is still ignored.
• Regular source file under a dot-prefixed ancestor (/home/user/.worktrees/project/functions/src/index.ts) is not ignored — the regression fix.
• Regular nested source file (lib/handlers/index.js) is not ignored.
• The functions directory itself is not ignored.
• No-op regression: a plain functions directory without any dot-prefixed ancestor still ignores .git/HEAD and still watches src/index.ts.

Also verified:

• npm run lint:quiet passes (eslint + prettier).
• npm run build passes.
• npx mocha src/emulator/functionsEmulatorShared.spec.ts — 20 passing (13 existing + 7 new).

Sample Commands

Not applicable — internal emulator behavior, no public CLI surface change.

[gemini-code-assist]

Code Review

This pull request fixes a bug in the Functions emulator where the file watcher would silently ignore changes if the project path contained a dot-prefixed ancestor directory (e.g., .worktrees/). The fix introduces a shouldIgnoreWatchPath utility that evaluates file paths relative to the functions directory before checking for hidden segments, ensuring that hidden ancestors do not trigger the ignore rule. Comprehensive unit tests were added to src/emulator/functionsEmulatorShared.spec.ts to cover various path scenarios. I have no feedback to provide.