fix: preserve launcher errors when package probes fail

[unbraind]

Fixes #135.

Canonical launcher catches inconclusive filesystem probe errors and preserves the original resolution diagnostic. Existing global lookup behavior is deliberately unchanged and documented.

PM item: ops-85at (available on main after merge).

Validation: 19 launcher cases pass on Node22.18/24.19/26.10; eight new regression cases fail before the fix. Full coverage on Node22.18 and26.10:455 passed,0failed,2existing skips,100% statements/branches/functions/lines across23sources. Typechecks,lint,duplication,docstrings,package,changelog,release-policy and PM health pass. Coverage used cached optional metadata and a temporary outside-repo launcher disabling implicit npm audits; no repository gate changes.

Pending: explicit production audit awaits user approval to transmit dependency metadata to npm; hosted CI/reviews still required. No release or downstream template propagation yet. Independent gate PRs #132/#134 are untouched.

Summary by Sourcery

Preserve launcher resolution errors when package presence checks cannot conclusively determine whether pm-ops is installed.

Bug Fixes:

• Preserve the original launcher resolution diagnostic when package presence probes encounter inconclusive filesystem errors instead of incorrectly treating the package as absent.
• Retain global package lookup behavior, including NODE_PATH resolution, while distinguishing absent packages from broken or uncertain installations.

Documentation:

• Document launcher behavior for unreadable or malformed lookup paths and global package lookup.

Tests:

• Add regression coverage for malformed, inaccessible, and global package lookup paths, including absent, broken, and working global installations.

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Summary by cubic

Fixes #135 by preserving the original installer resolution diagnostic when the launcher's package presence probe cannot conclusively determine whether pm-ops is installed.

Previously, an unreadable or malformed lookup path (e.g. ENOTDIR, ELOOP, EACCES, EPERM) raised a secondary filesystem error that replaced the original MODULE_NOT_FOUND message and could incorrectly trigger the omit-dev skip path. The probe now fails closed on inconclusive filesystem errors; Node's global lookup behavior, including NODE_PATH, is intentionally unchanged and documented.

Tests

• Adds regression coverage for local, hoisted, and global ENOTDIR/ELOOP failures, controlled EACCES/EPERM probe failures, and global absent, broken, and working package behavior.
• All 19 launcher cases pass on Node 22.18, 24.19, and 26.10; the eight new cases fail before the fix.

^{Written for commit e3e9618. Summary will update on new commits.}

[coderabbitai]

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[sourcery-ai]

Reviewer's Guide

The canonical launcher now fails closed when package-presence probes encounter inconclusive filesystem errors, preserving the original installer resolution diagnostic while retaining global Node lookup behavior. Documentation and comprehensive launcher regressions cover malformed permissions, path traversal failures, and NODE_PATH cases.

Sequence diagram for preserving launcher resolution errors

sequenceDiagram
    participant Launcher
    participant Resolver
    participant Filesystem

    Launcher->>Resolver: resolve(pm-ops/package.json)
    Resolver-->>Launcher: resolution error
    Launcher->>Resolver: resolve.paths(pm-ops/package.json)
    Resolver-->>Launcher: Node lookup paths including NODE_PATH
    loop each lookup path
        Launcher->>Filesystem: lstatSync(path to pm-ops, throwIfNoEntry false)
        alt package path exists
            Filesystem-->>Launcher: filesystem entry
        else path is absent
            Filesystem-->>Launcher: undefined
        else probe is inconclusive
            Filesystem-->>Launcher: filesystem error
            Launcher-->>Launcher: retain packagePresent
        end
    end
    alt package is present or probe is inconclusive
        Launcher-->>Launcher: rethrow original resolution error
    else package is absent
        Launcher-->>Launcher: skip optional package
    end

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File-Level Changes

Change	Details	Files
Preserve the installer’s original module-resolution diagnostic when package-presence probing is inconclusive.	Treat filesystem probe errors other than absence as evidence of uncertain presence and fail closed. Retain Node global lookup paths, including NODE_PATH, so local absence does not override installer resolution behavior. Document the revised launcher behavior and its distinction from unchanged global lookup semantics.	templates/prepare-merge-driver.ts README.md
Add regression coverage for malformed, inaccessible, and global package lookup paths.	Cover ENOTDIR, ELOOP, EACCES, and EPERM probe failures across local, hoisted, and global locations. Verify the original MODULE_NOT_FOUND resolution error is preserved and skip notices are not emitted. Verify absent, broken, and working packages discovered through NODE_PATH retain their expected behavior. Extend the test runner helper to pass environment variables and Node preload arguments.	test/merge-driver-launcher.test.ts
Record the associated PM work item and history metadata.	Add the ops-85at issue and JSONL history entries.	.agents/pm/issues/ops-85at.toon .agents/pm/history/ops-85at.jsonl

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#135	Make the package-presence probe robust to filesystem errors such as EACCES, EPERM, ENOTDIR, and ELOOP, treating an inconclusive probe as evidence of presence so the original resolution error is preserved.	✅
#135	Explicitly define and document whether Node global module lookup paths participate in the presence probe, while keeping the probe behavior consistent with installer resolution.	✅
#135	Propagate the corrected canonical launcher template through publication and downstream consumer copies that require byte-identical templates.	❌	The canonical template and README are updated, but the PR explicitly states that no release or downstream template propagation has occurred yet.

Possibly linked issues

• prepare-merge-driver probe: lstatSync only suppresses ENOENT, so an unreadable or looping ancestor node_modules crashes the prepare hook with a raw fs error #135: The PR catches lstat probe errors, fails closed, and preserves the original resolution error described by the issue.

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[greptile-apps]

Confidence Score: 5/5

[Medium risk] Fixes error handling in the package launcher probe logic.

The PR appears safe to merge based on the reviewed changes.

Summary

This PR makes the merge-driver launcher preserve its original resolution error when a filesystem presence probe is inconclusive, while retaining the absent-package skip and Node global lookup behavior.

• Adds local, hoisted, global, and controlled permission-error regression cases.
• Documents the launcher’s behavior for unreadable or malformed lookup paths.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Resolve preparation entry] -->|Success| B[Run installer]
  A -->|Failure| C[Probe package presence]
  C -->|Confirmed absent| D[Print notice and skip]
  C -->|Present or uncertain| E[Rethrow original resolution error]

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_{Reviews (2) · Last reviewed commit: "Merge branch 'main' into fix/launcher-pr..."}

[unbraind]

@sourcery-ai the review-budget notice is acknowledged (down-voted only because it carries no finding). @greptile-apps / @coderabbitai thanks — the 5/5 confidence summary and walkthrough match the launcher change; branch updated onto main after #132/#134 merged, waiting for checks.

[greptile-apps]

Thanks for the update. The refreshed branch and the #132/#134 merge context are noted. No additional findings from this review; the remaining prerequisites are hosted checks and approval for the production audit.

[coderabbitai]

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