explore: answer change questions from the diff
A question about the working changes ("what do my changes affect", "this branch", main..HEAD) is now answered from the diff. codegraph_explore and the Claude Code prompt hook read the merge base with the default branch plus uncommitted edits, or the named range. They map each hunk to the innermost indexed symbol it touches and lead with those symbols, most-called first, each with its callers and tests.
Agents never phrased an explore query this way: all 3 runs ran git diff through Bash, then explored symbol names. So the prompt hook, which sees the user's own words, is the channel that delivers it. The hook gate now accepts a confirmed change question.
Measured on this repo with #122 and #123 left uncommitted (Sonnet, 3 runs per arm, ledger 5.48). With the hook on, over 6 runs per arm: tool calls median 7 against 9.5, Read 0 against 4, time even (64 s against 67 s), and answers named more of the changed symbols.
The A/B harness gains AB_KEEP_GIT=1 (keep the target's .git) and AB_PROMPT_HOOK=1 (each arm runs its own build's prompt hook).
Checks: full vitest suite (306 files, 5197 tests), tsc --noEmit.