fix(agent-context): discover nested plan.md in scoped layouts (#3024)

[Noor-ul-ain001]

Summary

Fixes #3024. The agent-context updater discovered plan.md only one level deep (specs/*/plan.md), so scoped layouts created via SPECIFY_FEATURE_DIRECTORY — e.g. specs/<scope>/<feature>/plan.md — were never found, and no plan reference was written into the context file.

Changes

• bash (update-agent-context.sh): specs.glob("*/plan.md") → specs.rglob("plan.md").
• PowerShell (update-agent-context.ps1): one-level Get-ChildItem → -Recurse.
• PowerShell bug also fixed: the follow-up [System.IO.Path]::GetRelativePath(...) is .NET Core 2.1+ only and throws under Windows PowerShell 5.1 (.NET Framework). The exception was swallowed by the surrounding try/catch, leaving $PlanPath empty on 5.1 even when a plan was found — so nested discovery silently produced no plan reference on the most common Windows shell. Replaced with a direct root-prefix strip, matching the script's existing path helpers.

Tests

Added regression tests for both scripts (test_bash_script_discovers_nested_plan, test_powershell_script_discovers_nested_plan) asserting a specs/scope/001-feature/plan.md is discovered — which the old one-level glob would miss. The PowerShell test fails without the GetRelativePath fix and passes with it.

Verified locally: both new tests pass. Two unrelated bash tests in the same module (rejects_symlink_escape, deduplicates_context_files_in_order) fail only under Git-for-Windows MSYS bash and reproduce on clean main — pre-existing environment artifacts, not touched by this change.

[Copilot]

Pull request overview

Fixes the bundled agent-context extension’s plan auto-discovery so it can find plan.md in nested/scoped spec layouts (e.g. specs/<scope>/<feature>/plan.md) and correctly write a plan reference into the managed context section.

Changes:

• Bash updater: switches plan discovery from one-level globbing to recursive discovery under specs/.
• PowerShell updater: switches to recursive discovery and replaces a .NET-version-sensitive relative-path call with PS 5.1–compatible prefix stripping.
• Adds regression tests ensuring nested specs/scope/001-feature/plan.md is discovered by both updaters.

Show a summary per file

File	Description
tests/extensions/test_extension_agent_context.py	Adds regression tests covering nested/scoped plan discovery for bash and PowerShell updaters.
extensions/agent-context/scripts/powershell/update-agent-context.ps1	Updates plan discovery to recurse under specs/ and uses PS 5.1–compatible path relativization logic.
extensions/agent-context/scripts/bash/update-agent-context.sh	Updates plan discovery to recurse under specs/ for scoped layouts.

Review details

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• Files reviewed: 3/3 changed files
• Comments generated: 2
• Review effort level: Low

[mnriem]

Please address Copilot feedback

[Noor-ul-ain001]

Addressed both Copilot findings:

1. bash mtime fallback – symlink escape (update-agent-context.sh): the fallback filtered candidates lexically via relative_to(root) on the unresolved path, so a plan.md reached through a specs/ symlink pointing outside the project could be selected and emit an in-project-looking path. Candidates are now resolve()d and only those whose resolved path stays under root are kept before picking the newest.

2. PowerShell nested-plan test interpreter: the regression targets a Windows PowerShell 5.1 (.NET Framework) failure mode but ran whatever POWERSHELL resolved to (prefers pwsh). It now prefers powershell.exe on Windows (via a new WINDOWS_POWERSHELL constant + a powershell= param on the runner helper) so the 5.1-only compat fix is actually exercised, falling back to pwsh elsewhere.

Merged in the Copilot Autofix commit for #2 and reconciled it onto the helper-based approach to avoid duplicating the subprocess call. Both nested-plan tests pass locally (bash + Windows PowerShell 5.1).