fix(#829): gate claudex and close branch coverage gaps

docs/scratchpads/829-mutator-gate.md

@@ -71,3 +71,14 @@ Carried authority chain also verified/read for the locked T-B gate contract: SPE
 - BLOCKER 1 verified: first-class Claude/Pi route through `execLeaseGatedRuntime`, while the supported Claudex path preserves isolation but directly invokes `claude`; it therefore registers no anchor, injects no lease session, and the isolated config has no guaranteed all-tools gate hook.
 - BLOCKER 2 accepted: prior 88% was aggregate evidence. Remediation must produce independently measured branch coverage of at least 85% for each new executable (`launch-runtime.py`, `mutator-gate.py`, and daemon delta evidence), including successful exec-boundary collection and validation/error branches.
 - Remediation discipline: RED tests first; preserve the reviewed-good broker lock/state-transition ordering; update PR #837 on the same branch; no self-review or merge.
+
+### Remediation evidence
+
+- RED commit `046896c6`: both `mosaic claudex` and `mosaic yolo claudex` behavioral probes exited 1 because the direct path supplied neither a broker session nor the isolated all-tools hook; branch-focused Python tests failed on the absent injectable boundaries. Fresh WI-2 daemon-delta instrumentation also failed the ≥85% branch gate at 75%.
+- GREEN: Claudex now exposes only `execLeaseGated`, passes the preserved isolated proxy environment through the shared register-before-exec wrapper, and merges the exact `.*` mutator hook into isolated `settings.json` with mode `0600`. Missing broker/identity, malformed or symlinked settings, and an unverified consequential tool all fail closed. The broker transition/lock implementation was not changed.
+- Behavioral regression: normal and YOLO Claudex both receive a 64-hex broker session, retain their mode-specific arguments, observe the exact all-tools hook, and receive status 2 for unverified `Bash`.
+- Independent branch coverage: `launch-runtime.py` 16/18 = **89%** (statements 98%); `mutator-gate.py` 21/22 = **95%** (statements 99%); `daemon.py` WI-2 delta 35/40 = **88%** (whole-file branch 80%, statements 90%).
+- Fresh focused real-socket coverage run: WI-1 + WI-2 acceptance `46/46`; persistence `10/10`; branch unit suite `10/10`.
+- Fresh full repository suite: `43/43` Turbo tasks; `@mosaicstack/mosaic` `72/72` files and `1,381/1,381` tests.
+- Fresh root gates: typecheck `42/42`; lint `23/23`; format and `git diff --check` GREEN.
+- PR #837 remains open and unmerged. Terra CODE and Opus SECREV must both rerun from zero on the exact remediated head before coordinator-owned merge authorization.