[chrispezza]

The last of the four noisy hard rules. After a squash merge git branch -d refuses the branch, -D matched git-branch-force-delete, and in seatbelt every cleanup was denied (#122).

git branch -D merged-by-squash and git branch -D a-week-of-unpushed-work are the same string, so unlike #87 and #98 this could not be fixed by editing the rule. ADR-014 is the decision; it amends ADR-004.

What changed

• A hard rule may carry unless, naming a fact the engine does not establish. One value exists: branch_adds_nothing_to_default. The three force-delete entries in the bundled policy name it. A misspelt value is a load error.
• The hook asks git, after the entry has matched and only then. For each branch it runs git merge-tree --write-tree <remote default> refs/heads/<branch> and compares the tree with the default branch's own. A merge rather than a tree diff, because the default branch has usually moved on since the squash.
• When it holds, the entry is passed over and the call is judged like any other. It is not approved.
• Only a call that is the force delete and nothing else. A chain can change directory and the hook looks in its own, so cd x && git branch -D y, git -C, a variable, a glob and -r keep the entry's verdict. The deny reason now ends with the form that can pass, since the acting model reads it.
• The log line of a waived call carries hard_rule_waived. bouncer status reports a missing unless as a difference from the bundled entry.

The built hook, seatbelt, in a scratch repository (test/exemption.test.ts)

call	emitted
git branch -D squashed (squash-merged; default branch has moved on)	nothing, source: judge
git branch -D unmerged	deny
git branch -D squashed unmerged	deny
git checkout main && git branch -D squashed	deny
git branch -D squashed, policy without the unless line	deny

What it does not do

• A squash-merged branch whose lines the default branch later rewrote is still stopped. git cannot tell it from unmerged work, and asking the forge means a network call with credentials inside a hook.
• In a repository with no remote the exemption never holds. The base is a remote-tracking ref on purpose: against a local main, a commit that was only ever local would add nothing.

New surface, flagged

• The hook now runs git in the project directory, on force-delete calls only: symbolic-ref, rev-parse, merge-tree. Branch names reach git as arguments, never through a shell, and are restricted to [A-Za-z0-9._/-] not starting with - or ..
• merge-tree writes tree objects into the object database. No ref, index or working file changes; a test asserts that.
• The hook trusts the payload's cwd to be where the command runs. ADR-014 names that assumption.

Cost

• bench --against the base bundle with the base policy: paired median -0.4 ms judged, -0.7 ms hard-rule, 30 pairs. Calls that are not a force delete do not pay.
• Where git is asked: 90 ms median against 54 ms, 21 runs, mock backend.
• CACHE_VERSION 8 to 9, so each install recompiles its policy once.

For an existing install with a copied policy

Add unless: branch_adds_nothing_to_default to the three git-branch-force-delete entries. An older bouncer reading a policy with the key ignores it and stops every force delete.

Checks

1694 tests pass. Two holdout cases added, FROZEN updated in the same commit. HANDOFF.md updated.

Closes #122.

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