fix(build): correct billing error code in error-report docstring

[christian-byrne]

What

`_report_builder_error`'s docstring cited `SUBSCRIPTION_REQUIRED` as an example builder error code. comfy-builder never emits that code — it only emits `PAYMENT_REQUIRED` for billing refusals (`services/comfy-builder/apiserver/httpkit/billing_gate.go:44`, confirmed against current cloud `main`).

Why this matters

Agent-facing guidance (docstrings/comments agents read to decide how to react to a builder error) told them to match a code the server never sends, risking a permanent billing refusal being treated as an unmatched/retryable error by any caller trying to special-case it.

Verification

• `_builder_msg` (the actual error-body parser) has no hardcoded code matching — it passes the body's `error` field through verbatim, so runtime behavior already surfaced the real `PAYMENT_REQUIRED` string correctly. This is a documentation-only fix; no behavior change.
• Cross-checked against comfy-builder source: `PAYMENT_REQUIRED` is the only billing error code emitted (billing_gate.go, api.gen.go, releases/builds billing_gate_test.go).
• Full build test suite: 574 passed, 1 skipped.
• ruff clean.

Source: Linear BE-11190

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between 3fddc3e and dfb8c8f.

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• comfy_cli/command/build.py

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📝 Walkthrough

Walkthrough

The builder error documentation now identifies PAYMENT_REQUIRED responses instead of SUBSCRIPTION_REQUIRED. No exported or public entities changed.

Changes

Builder error documentation

Layer / File(s)	Summary
Update documented error response comfy_cli/command/build.py	The documented builder error body now uses PAYMENT_REQUIRED. A tiny wording fix, but the error name now fits the payment flow.

Suggested reviewers: guill, james00012

Merge Risk: ⚪ Minimal · up to dfb8c

This localized documentation-only change corrects the billing error code example without changing runtime behavior, and the reported checks pass; no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch christian-byrne/fix-build-error-code-docstring

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch christian-byrne/fix-build-error-code-docstring

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