fix(libsy): redact upstream bodies from error telemetry

[eugenn]

What

Failure telemetry recorded the raw upstream error body. record_client_error
took a &dyn Display and wrote LlmClientError's own text into the
libsy.client_call span, and libsy's record_run / record_llm_call wrote
LibsyError's text into the libsy.run / libsy.llm_call spans and their warn
logs. LlmClientError::UpstreamHttp renders as
upstream returned HTTP {status}: {body}, so a 4xx that quotes the request back
put conversation content into the trace and log pipeline for every failing turn:

error = client call to target "gpt-5.6-terra" failed: upstream returned HTTP 400
Bad Request: {"error":{"message":"Invalid 'input[1].content': ... <request text> ..."}}

The in-band streaming failures had the same shape: LlmResponseChunk::DecodeError
and LlmResponseChunk::StreamError recorded their message verbatim, and a
StreamError message is the text that becomes an UpstreamHttp body downstream.

This came out of the review of #610 (question 6: "whether tracing should also
redact the raw upstream response body, which is currently visible in the failing
call span").

How

libsy already had the vetted redaction for exactly this — safe_error_summary
/ safe_client_error in algorithms/util/robustness.rs, with exhaustive matches
so a new error variant cannot start leaking by omission. Rather than write a
second copy of those matches in switchyard-llm-client, this exports the pair
from switchyard_libsy (the crate switchyard-llm-client already depends on)
and routes all five recording sites through it.

record_client_error now takes &str instead of &dyn Display, so a caller
cannot hand it an unredacted error by accident. The two chunk arms pass a fixed
class string; error.type already carried the distinction (response_translation,
502), so nothing operational is lost.

What survives on the span: the failure class, the target or model it concerns,
and the HTTP status. What no longer does: the upstream body, boxed transport and
decode sources, and free-form messages.

Tests

crates/libsy-llm-client/tests/observability.rs:

• an_upstream_body_never_reaches_the_error_telemetry — drives a judge call that
  fails with a 400-style body carrying a content marker, then asserts the marker
  is absent from the libsy.client_call and libsy.llm_call spans and from every
  captured event, while upstream HTTP 500 and error.type = 500 remain.
• a_mid_stream_error_message_never_reaches_the_client_span — asserts the
  in-band stream error records error.type = 502 with a fixed summary.

Both fail on main's recording code (verified by reverting the redaction: the
span field comes back as upstream returned HTTP 500 Internal Server Error: {"error":{"message":"server error: <marker>"}}).

failed_call_records_error_outcome_and_warn_logs was updated for the same
reason: an external error's boxed source is unvetted, so libsy.run now carries
the label rather than the source text.

Gates run locally: cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace, uv run ruff check .,
uv run mypy switchyard, uv run pytest tests/.

Deliberately out of scope

Two other sites log error text and are left alone here:

• advisor_gate.rs fail-open warn and its advisor_review= audit record — that
  record already carries reply_head by design for benchmark tooling, so
  redacting only its error field would be a behavior decision about the audit
  format, not this fix.
• sse.rs stream-iteration warn — the same text is already returned to the
  requester in the error event, a different exposure than the shared telemetry
  pipeline.

Happy to fold either in if reviewers prefer.

Summary by CodeRabbit

• Bug Fixes

  • Improved error redaction in telemetry for model calls, streaming failures, and algorithm runs.
  • Prevented upstream error-body and in-stream content from appearing in logs and spans while retaining failure classifications.
  • Standardized recorded failure summaries to sanitized text.

• New Features

  • Exposed reusable helpers for generating safe, redacted error summaries.

[coderabbitai]

Walkthrough

The change applies redacted error summaries to Libsy and LLM client telemetry. It makes shared sanitization helpers public and adds tests for upstream HTTP errors, stream errors, and failed-run telemetry.

Changes

LLM error observability redaction

Layer / File(s)	Summary
Expose sanitization helpers and use them in Libsy telemetry crates/libsy/src/algorithms/util/robustness.rs, crates/libsy/src/lib.rs, crates/libsy/src/observability.rs	The sanitization helpers are public and re-exported. Run and model-call telemetry now records sanitized error summaries.
Redact client and stream errors crates/libsy-llm-client/src/observability.rs	Client-call and streaming telemetry now records redacted or fixed summaries. Decode and upstream stream errors retain their classifications without exposing message content.
Validate telemetry redaction crates/libsy-llm-client/tests/observability.rs	Tests verify that echoed HTTP error bodies and in-band stream errors do not appear in spans or logs. Failed-run assertions now expect "test failed".

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to 305ec

This change redacts error telemetry while preserving failure classifications. The remaining risk is limited to missing documentation for the newly public redaction helpers, which could lead to incorrect future use but does not affect the implemented redaction behavior.

Poem

A rabbit guards each error trail
With gentle paws, it hides the detail
Streams still show their class and state
Safe summaries pass the gate
Clean logs now dance beneath the moon

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 5 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: redacting upstream response bodies from error telemetry. This matches the pull request objectives and affected observability code.
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.

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Actionable comments posted: 1

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Inline comments:
In `@crates/libsy/src/algorithms/util/robustness.rs`:
- Line 24: Add Rustdoc comments for both public functions safe_error_summary and
safe_client_error in crates/libsy/src/algorithms/util/robustness.rs at lines
24-24 and 53-53, respectively; document that each returns a telemetry-safe
summary and excludes unconstrained error content.

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📒 Files selected for processing (5)

• crates/libsy-llm-client/src/observability.rs
• crates/libsy-llm-client/tests/observability.rs
• crates/libsy/src/algorithms/util/robustness.rs
• crates/libsy/src/lib.rs
• crates/libsy/src/observability.rs

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[afourniernv]

Thanks for catching this. I reproduced the leak, but I think this PR is doing too much in some places and not enough in others.

It makes the existing helper public and strips detail from every libsy error, while the server, Advisor, and SSE paths can still log raw messages.

I opened #615 to track the broader logging behavior. Could we keep this PR focused on the original libsy span leak and leave the helpers private?