fix: terminate fallible iterators after stream read failures

[digizeph]

Fixes #349.

Fallible iterators (into_fallible_record_iter, into_fallible_elem_iter,
into_fallible_update_iter, into_fallible_route_iter) now latch a spent input stream: a
framing IoError/EofError whose kind is not Interrupted or WouldBlock is yielded once
and followed by permanent None, and normal EOF ends iteration permanently too. The failed
decoder is never polled again.

Isolated malformed records stay skippable: body parse errors (including the IoError they
carry) do not end iteration, so the documented skip-the-error pattern keeps working for
corrupted records inside a healthy stream.

Implementation notes:

• Record framing and body parsing are separated on the fallible path
  (next_fallible_raw_record / next_fallible_record in src/parser/iters/mod.rs), so only
  framing read failures latch the stream.
• parse_chunked_record_with_zebra_compat in src/parser/mrt/mrt_record.rs is shared with the
  existing parse_mrt_record_with_zebra_compat instead of duplicating its parse-from-clone
  logic.

Regression coverage (tests/fallible_compressed.rs, offline and deterministic): damaged
bzip2/gzip streams terminate for all four iterator kinds after the intact records parse, within
bounded pulls; truncated compressed streams report one error and end; clean streams reach EOF;
malformed records and headers remain skippable; retryable reader errors do not end iteration;
a failed reader is not polled again.

No public API, signature, error-variant or dependency changes. The original real-world RIB was
not re-run; the committed regression uses synthetic damaged streams.

[Copilot]

🟡 Changes recommended

Partial reads followed by WouldBlock can leave retryable iteration permanently misaligned.

1 open finding

• Retryable partial reads can corrupt stream framing · New

What changed in this PR

Fixes non-terminating fallible iterators after fatal stream failures.

Changes:

• Separates MRT framing from body parsing.
• Latches fatal framing failures and EOF.
• Adds compressed-stream regression coverage.

File	Description
CHANGELOG.md	Documents corrected termination behavior.
src/​parser/​iters/​mod.rs	Adds shared framing and termination logic.
src/​parser/​iters/​fallible.rs	Applies termination state to record/element iteration.
src/​parser/​iters/​update.rs	Applies termination state to updates.
src/​parser/​iters/​route.rs	Applies termination state to routes.
src/​parser/​mrt/​mrt_record.rs	Extracts parsing of chunked records.
tests/​fallible_compressed.rs	Adds regression and error-handling tests.

🧠 Review effort: Balanced

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.06%. Comparing base (ec90671) to head (c10bd5f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #350      +/-   ##
==========================================
+ Coverage   92.04%   92.06%   +0.02%     
==========================================
  Files          96       96              
  Lines       23396    23401       +5     
==========================================
+ Hits        21534    21545      +11     
+ Misses       1862     1856       -6     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

🟢 Approval recommended

The implementation cleanly distinguishes fatal framing failures from skippable body errors and has comprehensive regression coverage.

0 open findings

1 resolved since last review

• Retryable partial reads can corrupt stream framing

🧠 Review effort: Balanced