fix: improve commit message reliability

[SnowCheetos]

Summary

Two root-cause fixes addressing issues found in real-world usage of autocommit on PR rust-osdev/acpi#306, where the maintainer noted that commit messages were confusing, hallucinated, and individual commits were not useful for review.

1. Literal model-free path for small diffs

Bypasses the LLM entirely for diffs under 20 lines across at most 2 files. The new literal_report() function in reduce.rs generates commit messages directly from diff structure:

• Counts additions and deletions
• Extracts symbol declarations from both added and removed lines
• Detects renames (same short prefix on added and removed symbol)
• Classifies as feat (additions only), refactor (removals/renames), fix (mixed), docs, or test
• Zero inference cost, zero hallucination risk

2. Version bumps only when manifest is explicitly changed

Changed should_evaluate in version_bump.rs to require the manifest file itself (Cargo.toml, package.json, etc.) to be in the diff. Previously, touching any source file in a crate would trigger a version bump suggestion, causing noisy suggestions on every intermediate commit within a PR.

Additional improvements

• Prompt rules now explicitly ban style: for any change touching executable code
• Analyze prompt warns when a chunk is under 15 lines: describe what was literally changed, do not infer intent
• Boilerplate risk notes (no security risks, no data loss) are filtered from commit output; risk section omitted when level is low
• --no-bump flag added as explicit opt-out for version suggestions

Files changed

• crates/core/src/pipeline/reduce.rs - literal_report() and helpers (add/delete counting, declaration extraction, classification)
• crates/core/src/pipeline/analyze.rs - route small diffs to literal path
• crates/core/src/llm/prompts.rs - better type classification rules, small-diff warnings
• crates/cli/src/cmd/version_bump.rs - only evaluate bumps when manifest changed
• crates/cli/src/cmd/commit.rs - --no-bump flag, boilerplate risk note filtering

[Copilot]

Pull request overview

This PR improves commit message reliability by introducing a model-free “literal” reporting path for very small diffs and by reducing noisy version bump recommendations unless a manifest file actually changes.

Changes:

• Add literal_report() (and helpers) to synthesize commit metadata directly from diff structure for small diffs, bypassing the LLM.
• Route DraftOnly + very small diffs through the literal path in analyze.rs.
• Tighten prompt guidance around type classification, small-diff behavior, and risk-note boilerplate; add --no-bump and filter boilerplate risk notes in commit output.
• Only evaluate version bumps when the manifest file itself is present in the diff.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
crates/core/src/pipeline/reduce.rs	Adds literal diff-to-report synthesis and tests; includes change classification and title/intent generation helpers.
crates/core/src/pipeline/analyze.rs	Routes very small DraftOnly diffs to the new literal report path; avoids moving key_symbols.
crates/core/src/llm/prompts.rs	Tightens prompt rules and injects a small-diff warning into analyze prompts.
crates/cli/src/cmd/version_bump.rs	Limits version bump evaluation to cases where the manifest file changed.
crates/cli/src/cmd/commit.rs	Adds --no-bump to skip bump logic and filters boilerplate risk notes / omits low-risk sections when empty.

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