fix(trpcagent): redact runner http errors

[XnLemon]

Objective

Redact runner-side tRPC-Agent HTTP status error details for Phase2 redaction closure.

Completed Changes

• Redact HTTP status error detail text before constructing runner errors.
• Cover both JSON error response bodies and plain-text response bodies.
• Fail closed if the shared platform redactor cannot initialize.
• Preserve request header sending behavior and non-sensitive diagnostic text such as HTTP status and stable error context.

Validation

• go test ./runner/trpcagent -run TestRunReturnsHTTPStatusError|TestRunReturnsHTTPStatusErrorRedactsPlainBody|TestDescribeReturnsHTTPStatusError|TestHTTPStatusErrorHandlesBodyReadErrorAndEmptyBody|TestErrorMessageFromBodyRejectsMalformedPayloads
• go vet ./runner/trpcagent
• git diff --check
• Subagent open-code-review first pass: 0 High / 0 Medium / 1 Low
• Subagent open-code-review final pass: 0 High / 0 Medium / 0 Low

Known Risks / Limitations

• This increment is scoped to runner-side HTTP status error formatting.

Follow-up Work

• Continue Phase2 closure by auditing remaining model-provider, graph, and gateway error surfaces.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 6c161a51-425b-4194-b521-3ade8292f609

📥 Commits

Reviewing files that changed from the base of the PR and between 361e2a4 and 5c2a57e.

📒 Files selected for processing (2)

• runner/trpcagent/runner.go
• runner/trpcagent/runner_test.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/phase2-trpcagent-runner-error-redaction

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