fix(mcp): exit the CLI cleanly on a broken-pipe stdout/stderr error

[bitfathers94]

fix(mcp): exit the CLI cleanly on a broken-pipe stdout/stderr error

process.stdout/stderr had no "error" listener, so a broken pipe (EPIPE) —
the downstream reader in ... | head closing after a few bytes while the
CLI is still writing a large payload — surfaced as an uncaught write EPIPE
and crashed the whole CLI with a stack trace. flushStdio() only drained via
the "drain" event, which never fires once the stream has errored.

Attach an "error" listener to both streams (gated on the launched-CLI
entrypoint) that exits cleanly: success on EPIPE (a normal end to a piped
command), a conventional failure code otherwise. Normal, fully-drained
output is unchanged.

Closes #8691

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.29%. Comparing base (fac2222) to head (98e150d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8731      +/-   ##
==========================================
- Coverage   90.56%   82.29%   -8.27%     
==========================================
  Files          96       97       +1     
  Lines       22490    24750    +2260     
  Branches     3884     4742     +858     
==========================================
  Hits        20367    20367              
- Misses       1945     4205    +2260     
  Partials      178      178              

Flag	Coverage Δ
backend	0.00% <ø> (?)

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Files with missing lines	Coverage Δ
packages/loopover-mcp/bin/loopover-mcp.ts	0.00% <ø> (ø)

[loopover-orb]

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✅ LoopOver review result - approve/merge recommended

_{Review updated: 2026-07-26 01:27:45 UTC}

2 files · 1 AI reviewer · no blockers · readiness 93/100 · CI green · clean

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This adds an "error" listener on process.stdout/stderr, gated on the launched-CLI entrypoint, that exits 0 on EPIPE and 1 otherwise, fixing the uncaught-exception crash from a broken pipe (e.g. `| head`). The fix is correctly placed at the source (the streams themselves) rather than patching a symptom, and the added test spawns the real compiled CLI piped into a reader that closes early to reproduce the actual OS-pipe race rather than fabricating a payload. Placement right after flushStdio() and gating on runAsCliEntrypoint is consistent with the rest of the file's conventions for entrypoint-only side effects.

Nits — 4 non-blocking

• The listener calls process.exit() directly from inside the error handler without draining any already-buffered writes on the other stream (e.g. an EPIPE on stdout could still race with a pending stderr write), though this is unlikely to matter in practice given the immediate process.exit semantics.
• The 1705-line file continues to grow with this change; consider whether entrypoint-lifecycle concerns like this belong in a small dedicated module, per the file's own noted 1:1-conversion design debt.
• Consider whether process.exitCode = ... plus a natural return would be safer than process.exit() inside an async-context error handler, though for this synchronous stream-error case it's likely fine.
• The v8 ignore comment block is thorough and clearly explains why the branch is untestable in-process — good precedent to follow for other entrypoint-gated code in this file.

Decision drivers

• ✅ Code review — No blockers (1 reviewer)
• ✅ Gate result — Passing (No configured blocker found.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#8691
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (1 linked issue).
Validation posture	⚠️ 20/25	Preflight is ready, but the PR body does not name the validation run.
Contributor workload	✅ 10/10	Author activity: 44 registered-repo PR(s), 28 merged, 0 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	bitfathers94; Gittensor profile; 44 PR(s), 0 issue(s).
Improvement	✅ Minor	risk: clean · value: minor · LLM: moderate

Linked issue satisfaction

Addressed
The diff attaches an "error" listener to both process.stdout and process.stderr that exits cleanly (0 on EPIPE, 1 otherwise) instead of crashing, gated on the CLI entrypoint, matching the fix location and requirement in the issue.

Review context

• Author: bitfathers94
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: TypeScript
• Official Gittensor activity: 44 PR(s), 0 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Start here: Add validation command/output.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

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_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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LoopOver approves — the gate is satisfied and CI is green.