---
id: review-002-fu-stream-error-coverage
name: Streaming error-arm coverage — forward_stream invalid input, PEM read-failure, over-cap poll_write mirror (post-bulk coverage gap)
status: done
depends_on: []
scope: narrow
risk: low
impact: component
level: implementation
tags: [infra, review-002, follow-up, coverage]
---

## Description

Bracketed follow-up discovery from the post-bulk coverage re-pass
(95.89% regions overall; the review-002 bulk's own new code verified
fully covered — PRJ-16 guard, body cap, router reorder, batch cap,
WS-13/18/19, the OAI-11 memo node-budget all exercised). The residue
is small but one item matters more than its line count:

- **`forward_stream` build-request error arm** (forward.rs:1085-1090):
  a Sub op invoked with an invalid input (undeclared key, non-scalar
  placeholder value) must produce exactly one error envelope from the
  stream — the streaming analog of the Once-path error handling. No
  test drives it: every SSE test (from_jsonschema `integration_sse_subscription…`,
  forward.rs's stream family) sends valid input. A regression returning
  an empty stream (silently swallowing the error) would be invisible —
  and an empty-200-subscribe is the worst failure shape for a
  subscriptions consumer.
- **PEM read-failure arms** (http_client.rs CaBundleRead/ClientCertRead,
  sync + async): the *parse*-failure arms are covered
  (`corrupt_ca_bundle_fails_ca_bundle_parse_with_path`,
  `garbage_client_cert_fails_…` in client_tls.rs, landed in 6490d15),
  but the **unreadable-file** arms (nonexistent path, unreadable
  permissions) have no test on either build path. The error taxonomy
  half-documented at `HttpClientBuildError`'s doc block (:214) is
  half-specified.
- **Over-cap `poll_write` rejection** (byte_adapter.rs:789-798): WS-14's
  moved check rejects writes *above* `PENDING_BUFFER_CAP` with
  `InvalidData` before entry to the queue — the "at cap" boundary is
  tested (`tungstenite_write_at_the_cap_is_accepted`, 1158) and the
  framing-level cap-trip is tested both flavors
  (`axum_framing_cap_trip…`), but the single-call over-cap rejection
  itself (the WS-14 acceptance test's own criterion) never runs: no
  test writes `PENDING_BUFFER_CAP + 1`.
- **`forward_stream` SSE-parser residual edges**: split-CRLF-across-
  chunks (the `\r` + `"\n…"` case), invalid-UTF8-line drop — the
  parser edges the bulk's stream arms work next to.
- **`from_value` structural rejections** (openapi_spec.rs:391-398,
  416-418): a non-object document, a missing-`info`, a non-object
  `paths` — none ever exercised (all other structural rejects are).
- **Connection-failure arms**: `protocol_handler` accept-path
  `stream_error_to_handler` (adapter.rs:597-599) and the read-pump
  demux-gone `break` (byte_adapter.rs:374-381) — both are
  connection-failure semantics with zero direct coverage.
- **Dead-ish**: `impl Default for WsTimeouts` (upgrade.rs:344-351)
  has zero callers (the extension is constructed explicitly in the
  one test that uses it) — delete or `#[allow(dead_code)]` with the
  reason.

## Acceptance Criteria

- [ ] Wire test: Sub op + undeclared key (or non-scalar placeholder
      value) → the subscriber receives exactly one `INVALID_INPUT`
      envelope and the stream ends (upstream receives zero requests)
- [ ] Two PEM read-failure tests: `SharedHttpClient::new` with a
      nonexistent CA path → `CaBundleRead` carrying the path;
      `reload` with a nonexistent client-cert path → `ClientCertRead`
- [ ] One over-cap `poll_write` test: `write_all(PENDING_BUFFER_CAP+1)`
      → `InvalidData` error naming the cap (asserts the WS-14 moved
      check's rejection leg; the = cap test exists)
- [ ] SSE parser edge tests: CRLF split across chunks (`…\r` ends
      chunk 1, `\n…` opens the next), invalid-UTF8 line dropped
- [ ] from_value structural tests: non-object doc, missing-`info`,
      non-object `paths` → `SchemaParse` naming the missing member
- [ ] `WsTimeouts` redundant `Default` deleted (or justified+allowed)
- [ ] `cargo llvm-cov --all-features`: named arms no longer dark;
      `cargo test --all-features`, clippy, fmt pass

## References

- docs/reviews/002-post-remediation-review.md (Part G' test-gaps; post-bulk re-analysis finding list)
- src/adapters/forward.rs:1085-1090 (stream build-error arm), src/client/http_client.rs:484-545 (read-failure arms), src/websocket/byte_adapter.rs:789-798 (over-cap poll_write)
- tests/client_tls.rs (the PEM harness: parse-failure tests at :226-448 are the pattern to mirror for read-failures)
- tasks/infra/review-002-cov-deployment-knobs.md (the pre-bulk coverage task these extend)
- tasks/infra/review-002-cov13-dead-code.md (the dead-code convention for the WsTimeouts Default)

## Notes

Tests-only + one deletion. The streaming-build-error test's
load-bearing assertion is the *single envelope then end* semantics —
mirror `oversized_upstream_sse_line_terminates_with_one_internal_envelope`'s
assert structure but trigger pre-send instead (invalid input, no
responder needed for the reject case — wire it against a live-responder
anyway if the harness makes it cheap; the zero-upstream-contact assert
is the point). The `spawn_responder`-family harnesses in
forward.rs/from_jsonschema.rs cover the seam.