fix(tool): evaluate grep permissions on requested path

[Astro-Han]

Summary

Fix grep external-directory permission evaluation so an allowed requested alias or symlink path is honored while grep still searches the resolved real path.

Why

A grep path can be a user-approved alias that resolves outside the project. Before this change, grep resolved the path before asking for external_directory, so permission rules written for the requested alias could still prompt or deny based on the real path.

Related Issue

Ports the behavior from upstream anomalyco/opencode#26958. There is no local PawWork issue for this narrow upstream-value PR.

Human Review Status

Pending

Review Focus

Please check the permission boundary: only grep opts into requested-path permission patterns, while the default shared helper behavior for shell/read/write remains realpath-based.

Risk Notes

Permissions/path behavior changed for grep. No visible UI changed, so the UI check is not applicable. No docs, release notes, dependencies, credentials, deletion behavior, generated content, or local file changes are included. I considered macOS and Windows path impact; the regression test covers POSIX symlink behavior and the implementation uses the existing Windows path normalizer for the new optional permission path.

How To Verify

RED: bun test test/tool/grep.test.ts failed on the new alias-path permission regression because grep requested external_directory for the real path.
Focused grep tests: bun test test/tool/grep.test.ts -> 10 pass, 0 fail.
Shell symlink guard: bun test test/tool/shell.test.ts --test-name-pattern "asks for real external_directory when bash reads through tmp symlink" -> 1 pass, 53 filtered out, 0 fail.
Typecheck: bun run typecheck in packages/opencode -> passed.
External-directory helper tests: bun test test/tool/external-directory.test.ts -> 14 pass, 0 fail.
Review follow-up guard: bun test test/tool/shell.test.ts --test-name-pattern "asks for real external_directory when bash reads through tmp symlink" -> 1 pass, 53 filtered out, 0 fail.
Diff check: git diff --check -> passed.

Screenshots or Recordings

Not applicable; no visible UI changed.

Checklist

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• (conditional) I considered macOS and Windows impact for platform, packaging, updater, signing, paths, shell, or permissions changes. Leave unticked only if no platform/packaging surface was touched.
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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: e1f0d7a4-4e26-494c-a4cc-24a6a0b9b808

📥 Commits

Reviewing files that changed from the base of the PR and between aff7ce2 and 6506ee5.

📒 Files selected for processing (3)

• packages/opencode/src/tool/external-directory.ts
• packages/opencode/src/tool/grep.ts
• packages/opencode/test/tool/grep.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/c2-grep-permission

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[github-actions]

Suggested priority: P2 (includes non-doc, non-test paths outside the low-risk bucket).

P1/P0 are reserved for maintainer confirmation. Please relabel manually if this is a release blocker, security issue, data-loss risk, or updater/runtime failure.

[gemini-code-assist]

Code Review

This pull request updates the grep tool to use the requested alias path rather than the resolved path when checking external_directory permissions, and adds a corresponding test case. The reviewer suggests simplifying this implementation by replacing the permissionPath string option with a boolean flag checkRequestedPath. This change would allow reusing the already computed and normalized path, eliminating duplicated path resolution logic, and avoiding unnecessary path normalization when classifying permission rule patterns.

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[Astro-Han]

Addressed the Gemini implementation-shape suggestion in f89677f: assertExternalDirectoryEffect now uses a narrow checkRequestedPath boolean instead of a generic path override, reusing the already-normalized requested path while preserving the default realpath behavior for other callers.