fix: S12.23 PassthroughBuffer error path completeness

[DavidCozens]

Summary

• Guards SolidSyslogPassthroughBuffer_Create against a NULL sender at entry, returning the shared SolidSyslogNullBuffer fallback and emitting a new PASSTHROUGHBUFFER_ERROR_NULL_SENDER code instead of crashing on the first subsequent Write.
• Adds three pinning tests for the NULL-sender contract (ERROR reporting, fallback distinct from any pool slot, no pool-slot consumption) and one for the already-safe Destroy(NULL) fallthrough.
• Removes the IGNORE_TEST(SolidSyslogPassthroughBuffer, HappyPathOnly) placeholder — every referent is now pinned or out of scope per the story spec. This was the last IGNORE_TEST in the codebase.

Closes #444. Sibling of S12.07 / #443.

Test plan

• Local: cmake --build --preset debug && ctest --preset debug — green
• Local: cmake --build --preset clang-debug && ctest --preset clang-debug — green
• Local: cmake --build --preset sanitize && ctest --preset sanitize — green
• Local: cmake --build --preset tidy — green
• Local: cmake --build --preset coverage --target coverage — Core/Source/SolidSyslogPassthroughBuffer*.c at 100%
• Local: cmake --build --preset iwyu --target iwyu — green
• Local: clang-format --dry-run --Werror over changed files — green
• CI: analyze-cppcheck (both plain and --addon=misra) — runs in container with cppcheck available

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved robustness of buffer creation to gracefully handle null input parameters. The system now returns a fallback buffer and reports a descriptive error instead of failing.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b3b6e697-a9ac-4a65-8d48-df61a4239814

📥 Commits

Reviewing files that changed from the base of the PR and between a0edced and f18cd20.

📒 Files selected for processing (4)

• Core/Interface/SolidSyslogPassthroughBufferErrors.h
• Core/Source/SolidSyslogPassthroughBufferMessages.c
• Core/Source/SolidSyslogPassthroughBufferStatic.c
• Tests/SolidSyslogPassthroughBufferTest.cpp

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📝 Walkthrough

Walkthrough

This PR adds NULL sender validation to the passthrough buffer creation function. When SolidSyslogPassthroughBuffer_Create is called with a NULL sender, it now emits PASSTHROUGHBUFFER_ERROR_NULL_SENDER and returns a fallback null buffer instead of proceeding with pool allocation.

Changes

NULL Sender Validation

Layer / File(s)	Summary
Error contract definition Core/Interface/SolidSyslogPassthroughBufferErrors.h, Core/Source/SolidSyslogPassthroughBufferMessages.c	New PASSTHROUGHBUFFER_ERROR_NULL_SENDER enum value and its corresponding error message string mapping define the error code emitted when a NULL sender is passed to Create.
NULL sender guard implementation Core/Source/SolidSyslogPassthroughBufferStatic.c	SolidSyslogPassthroughBuffer_Create initializes the handle from the null buffer, explicitly checks if sender is NULL, returns the fallback buffer and emits the error if true, otherwise preserves existing pool acquisition and initialization logic.
Test coverage for NULL sender handling Tests/SolidSyslogPassthroughBufferTest.cpp	Test includes are updated to support error handler assertions; new destroy test validates null handle behavior; three pool-level tests verify NULL sender Create reports the error, returns a distinct fallback handle, and does not consume pool slots.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related issues

• S12.23: PassthroughBuffer error path completeness #444: Implements the same fix—adds PASSTHROUGHBUFFER_ERROR_NULL_SENDER enum value, guards Create against NULL sender, returns the null buffer fallback, adds error message, and includes comprehensive validation tests.

Poem

🐰 A sender NULL arrives one day,
The buffer gracefully says "nay!"
With fallback grace it bows and bends,
And logs the error to all its friends.
No pool slots wasted, all is well—
The rabbit hops and rings the bell! 🔔

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding error path completeness to PassthroughBuffer, specifically the NULL sender guard.
Description check	✅ Passed	The description is comprehensive and well-structured, covering Purpose (issue #444), Change Description (NULL-sender guard, new error code, test additions), Test Evidence (multiple test plans executed), and Areas Affected (PassthroughBuffer module).
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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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/s12-23-passthrough-buffer-error-paths

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[github-actions]

☀️   Quality Summary

   🚦   build-linux-gcc: 100% successful (✔️ 1330 passed)
   🚦   build-freertos-host-tdd: 100% successful (✔️ 1558 passed)
   🚦   build-linux-clang: 100% successful (✔️ 1282 passed)
   🚦   sanitize-linux-gcc: 100% successful (✔️ 1282 passed)
   🚦   integration-linux-openssl: 100% successful (✔️ 9 passed)
   🚦   integration-linux-mbedtls: 100% successful (✔️ 7 passed)
   🚦   integration-windows-openssl: 100% successful (✔️ 9 passed)
   🚦   bdd-linux-syslog-ng: 94% successful (✔️ 46 passed, 🙈 3 skipped)
   🚦   bdd-windows-otel: 90% successful (✔️ 44 passed, 🙈 5 skipped)
   🚦   bdd-freertos-qemu: 86% successful (✔️ 42 passed, 🙈 7 skipped)
   🚦   build-windows-msvc: 100% successful (✔️ 1141 passed)
   🚦   build-linux-tunable-override: 100% successful (✔️ 1282 passed)
   ⚠️   Clang-Tidy: No warnings
   ⚠️   CPPCheck: 1 warning (low: 1)

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Created by Quality Monitor v1.14.0 (#f3859fd). More details are shown in the GitHub Checks Result.