fix(agents): re-resolve the pi entry at spawn time after upgrades

[Alan-TheGentleman]

Closes #1568

PR type

• Bug fix
• New feature
• Documentation only
• Code refactoring
• Maintenance/tooling
• Breaking change

Summary

• Subagents failed with MODULE_NOT_FOUND for the rest of a Gentle Shell session after pi was upgraded mid-session. piCommand() captured the parent's absolute cli.js path once at extension load, and package managers (e.g. pnpm global/v11/<hash>) delete that directory on upgrade.
• The runner now re-resolves the pi command immediately before each child spawn. It keeps the running entry while it exists and falls back to the pi PATH shim when it has been removed. GENTLE_PI_AGENTS_PI precedence is unchanged.

Changes

File	Change
lib/agents-runner.ts	piCommand accepts an existence check; the runner uses an optional resolvePi() per spawn
extensions/gentle-agents.ts	Wires resolvePi into production deps
tests/agents-runner.test.ts	Existing/missing entry, non-cli.js entry, override precedence, and an entry disappearing between two spawns

Test plan

• node --experimental-strip-types --test tests/agents-runner.test.ts tests/agents-runner-process.test.ts: 80/80 passed. The new regressions failed before the fix (2 expected failures).
• node scripts/check-types.mjs: baseline gate passed, 187 recorded diagnostics, no regressions.
• node scripts/build-runtime-modules.mjs --check: passed (agents-runner is not a generated runtime source).
• git diff --check: passed.
• Reproduced in a live session: after a pnpm upgrade of pi, every subagent launch failed with MODULE_NOT_FOUND until the removed path was recreated by hand.
• Full pnpm test was not run locally; CI covers it.

Known limit: the fallback needs pi on PATH, and an entry removed between the existence check and the spawn is still a (tiny) race.

Summary by CodeRabbit

• Bug Fixes
  • Agent launches now select an available command and fall back to the standard command when needed.
  • The command is rechecked for each launch, so changes in availability are handled.
• Configuration
  • Added support for overriding the command used to launch agents.
  • When the current Node.js entry point is an eligible, existing CLI entry, it can be used to launch agents.

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Reviewing files that changed from the base of the PR and between 6d633c0 and 5813b31.

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• extensions/gentle-agents.ts

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📝 Walkthrough

Walkthrough

The runner now resolves the Pi command when it starts each child process. The resolver checks a trimmed environment override or reuses the current Node executable and CLI entry when that entry exists. Otherwise, the runner uses its configured pi command.

Changes

Pi command resolution

Layer / File(s)	Summary
Pi command selection lib/agents-runner.ts	RunnerDeps gains an optional command resolver. The exported piCommand checks a trimmed environment override, then reuses an eligible existing cli.js entry, and otherwise falls back to pi.
Per-spawn resolution and tests extensions/gentle-agents.ts, lib/agents-runner.ts, tests/agents-runner.test.ts	The extension supplies a resolver, and AgentRunner.launch calls it for each spawn. If it returns no command, the runner uses the configured pi command. Tests cover command selection and a CLI entry that disappears between spawns.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: decode2

Merge Risk: 🟡 Moderate · up to 5813b

On Windows installations where pi is available only through a .cmd shim, subagent launches can still fail after an upgrade. Address or explicitly accept this remaining gap before merging.

Architecture Summary

Architecture risk: 🔵 Low · up to 5813b

The change affects 3 systems.

Changed systems: extensions, lib, tests

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — extensions (service) was modified; 1 changed file maps to changed impact.
• observed — lib (service) was modified; 1 changed file maps to changed impact.
• observed — tests (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in lib/agents-runner.ts: Adds the node:fs existsSync import used to verify whether the current CLI entry exists.
• observed — Modified behavior in lib/agents-runner.ts: Adds optional RunnerDeps.resolvePi, which can supply the command used to start child processes.
• observed — Modified behavior in lib/agents-runner.ts: Adds exported piCommand: a non-empty trimmed environment override is split into a command and arguments; otherwise, a matching cli.js entry is reused through the current Node executable only when it exists. The previous behavior reused any matching entry without checking existence.
• observed — Modified behavior in lib/agents-runner.ts: AgentRunner.launch now uses resolvePi() when provided and falls back to deps.pi when it is absent or returns no command; previously it always used deps.pi.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: resolving the pi entry at spawn time to support upgrades during an active session.
Linked Issues check	✅ Passed	The changes meet the coding objective in #1568. AgentRunner.launch resolves the pi command for each spawn. piCommand reuses the current cli.js entry only when it exists, then falls back to the `…
Out of Scope Changes check	✅ Passed	The changes stay within #1568. Production changes update pi command resolution for subagent launches. Test changes verify command selection and per-spawn resolution. No unrelated behavior is demonstra…

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Actionable comments posted: 1

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Inline comments:
Review comments at @extensions/gentle-agents.ts:
- Line 120: Update the `resolvePi`/`piCommand` fallback so Windows can launch
the installed CLI when the parent `cli.js` entry is unavailable, using a
Node-resolved entry or Windows shim handling that preserves argument quoting and
IPC. Add a regression test covering the Windows fallback.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 2f37fac1-3e9e-4ca0-bb5c-af6182808546

📥 Commits

Reviewing files that changed from the base of the PR and between 4b6b148 and 6d633c0.

📒 Files selected for processing (3)

• extensions/gentle-agents.ts
• lib/agents-runner.ts
• tests/agents-runner.test.ts

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 3 remain after this review.