Harden a change

A green test suite does not prove that a change is correct. Defects hide where example tests do not look: cross-layer seams, state-machine interleavings, hard limits, and unit boundaries.

Read AGENTS.md first. Load the tigerstyle, code-simplification, and adversarial-code-review skills. This skill applies their rules.

Setup

• The default scope is git diff main...HEAD. The user can narrow it.
• Edit in a new worktree (git worktree add -b harden/<topic> ../ot-harden-<topic> HEAD). Do not use git stash. All worktrees share the stash, and it holds the user's work.
• Before you edit, run the affected suites and record the pass and fail counts. Then you know which later failures are new. The commands are in references/coverage-tools.md.
• Run checks in the foreground. Do not end a turn while a background job runs.

Step 1: measure what no test reaches