Smart Token Budgeting & Large Diff Truncation for Large Commits

Start by reading the staged-diff handling in internal/git and the configuration surfaces config.env and .git-commit-summary.yaml. Use mock large diff inputs to understand the required internal/git tests. Done means oversized diffs stay within configured limits, lockfiles and generated files are collapsed, and the related configuration or CLI option is covered by tests.

Problem Statement

When working on large commits (such as updating dependency lockfiles (go.sum, package-lock.json), large code refactors, or bulk file additions), the raw git diff can easily exceed LLM context windows or unnecessarily consume a large number of input tokens. Currently, git-commit-summary sends the entire raw diff to the LLM provider.

Proposed Feature: Smart Token Budgeting & Large Diff Truncation

Implement a preprocessing step for staged diffs that ensures large changes fit comfortably within LLM token limits while retaining the essential semantic summary of the changes.

Detailed Outline Plan

1. Diff Statistics & Token Estimation:

   • Parse the git diff output into file-level chunks (internal/git).
   • Implement a lightweight token estimator (e.g., character-to-token heuristic or using a tokenizer helper) to gauge the size of each file diff.

2. Diff Prioritization & Truncation Strategy:

   • Lockfiles & Generated Files: Automatically collapse or omit full diffs for well-known generated files / lockfiles (go.sum, package-lock.json, pnpm-lock.yaml, minified assets), replacing them with a summary line (e.g., ... (lockfile updated: X dependencies added, Y removed)).
   • Code Files: If total diff exceeds a configured threshold (e.g., max token limit or max line count):
     • Prioritize core logic files over documentation or tests, or truncate individual file diffs after a maximum number of hunks/lines, appending a truncation notice (e.g., ... [diff truncated for length]).

3. Configuration & Flags:

   • Add configuration options (in config.env / .git-commit-summary.yaml) for max diff tokens / size thresholds.
   • Add CLI flag support if needed (e.g., --max-diff-tokens).

4. Testing & Validation:

   • Add unit tests in internal/git for diff truncation and lockfile collapsing logic.
   • Verify behavior against mock large diff inputs.