fix(commons): contain tool-calling proto exceptions

[shubhamsinnh]

Summary

• contain allocation and unexpected exceptions across tool-call parsing, prompt formatting, and validation proto entry points
• use scoped ownership for parsed calls, validation results, and temporary prompt buffers so unwinding cannot leak partial C allocations
• protect the initial and follow-up prompt builders and the JSON normalization helper used beneath the proto APIs
• include the previously unguarded rac_tool_call_validate_proto path identified during the entry-point audit

Dependency

This is a stacked draft based on the current head of #740. The issue-specific change is commit dc1e1be89. Until #740 merges, GitHub will also show its seven parent commits in this PR. This branch will be rebased onto updated main and revalidated before the PR is marked ready.

Validation

• protobuf-enabled C++20 translation-unit compilation with warnings treated as errors
• protobuf-disabled C++20 translation-unit compilation with warnings treated as errors
• diff whitespace validation
• no added lines over the repository's 100-column limit

No new tests were added. A clean configure for the existing behavioral target was stopped during unrelated Windows archive dependency capability probes before project compilation.

Fixes #867

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of memory allocation failures during tool-call processing.
  • Allocation failures now return explicit out-of-memory errors instead of being treated as successful operations with empty results.
  • Unexpected processing errors now return a clear internal error status.
  • Improved cleanup of temporary tool-call data to reduce the risk of resource leaks.
  • Tool-call format reporting now accurately reflects the format used after fallback processing.

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• core/src/features/llm/tool_calling.cpp

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• core/src/features/llm/tool_calling.cpp

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📝 Walkthrough

Walkthrough

The change adds explicit parser statuses, RAII ownership, and exception handling across JSON parsing, tool-call parsing, validation, and prompt-building entry points. Allocation and internal failures now return error codes instead of being treated as no matches or escaping C boundaries.

Changes

Tool-calling error containment

Layer / File(s)	Summary
Parser status and ownership core/src/features/llm/tool_calling.cpp	Parsing helpers distinguish no match, success, out-of-memory, and internal-error states. RAII wrappers manage allocated results, strings, tool calls, and validation values.
Format parsing status propagation core/src/features/llm/tool_calling.cpp	Tool extraction and format parsers propagate allocation and normalization failures. Partial outputs are cleared on failure.
Format entry-point error mapping core/src/features/llm/tool_calling.cpp	Normalization and formatted parsing map parser failures and exceptions to exported error codes. Successful LFM2 fallback reports the default format.
Protocol ownership and exception boundaries core/src/features/llm/tool_calling.cpp	Protocol parsing, validation, and prompt formatting use RAII buffers and exception boundaries. Parallel-call errors are propagated.
Public prompt-building boundaries core/src/features/llm/tool_calling.cpp	Public prompt-building functions initialize output pointers and map allocation or unexpected exceptions to error codes.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix · Severity of issue fixed: Medium

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 21.05% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 57 functions across 1 files.	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 identifies the main change: containing exceptions in commons tool-calling protocol code.
Description check	✅ Passed	The description provides a clear change summary, dependency context, validation details, test limitations, and linked issue. It does not use the template headings for Type of Change, Labels, or Checkl…
Linked Issues check	✅ Passed	The reviewed changes satisfy the coding requirements in [#867]. The exported proto parsing, prompt formatting, initial-prompt, and follow-up-prompt paths use exception boundaries. The handlers map `st…
Out of Scope Changes check	✅ Passed	The reviewed changes are limited to core/src/features/llm/tool_calling.cpp. Parser status propagation, ownership wrappers, error mapping, prompt-buffer ownership, and exception boundaries directly s…

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Actionable comments posted: 2

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Inline comments:
In `@core/src/features/llm/tool_calling.cpp`:
- Around line 1798-1800: Update the fallback path in the tool-calling parser
around parse_default_format so the effective format is tracked separately from
the initial LFM2 format; when the default parser succeeds after kNoMatch, set
the result metadata to RAC_TOOL_FORMAT_DEFAULT before populating out_result,
while preserving LFM2 for successful LFM2 parses.
- Around line 1715-1716: Update the normalization-result handling in the
tool-call parser to return a new internal-error parser status when
rac_tool_call_normalize_json returns RAC_ERROR_INTERNAL, while preserving
kNoMatch for ordinary non-success results. In rac_tool_call_parse_with_format,
map kInternalError to RAC_ERROR_INTERNAL so the failure is propagated instead of
returning the original text with RAC_SUCCESS.

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