v1.106.0 — mux-runner review fixes + test-isolation (R-WTIV) + integration-test hardening (R-ITIH)

Mux-runner reliability (ultracode review): 8 confirmed findings fixed — M1 exit-path commit scopes staging to ticket-owned paths; M2/M3/L1 source-progress seam (first-spawn seed, null sentinel, OR-based probe guard); M4 read-error logging; L2 idle-stall recovery cap; L5 null-ticket clean exit; L6 recovery-ladder parity.

R-WTIV test-isolation: a test (gate-skip-activity-events) no longer commits the REAL repo via working_dir: REPO_ROOT — now uses a tmp git working_dir.

R-ITIH #109 integration-test hardening: AC-1 audit-test-isolation.sh working-tree guard (flags working_dir: REPO_ROOT/process.cwd() in session-bin spawns); AC-2 mux-runner validate-or-halt on missing working_dir (new state_working_dir_missing exit) + PICKLE_TEST_MODE git-mutation assertion in commitAndContinueDoneFlip/resetToSha; AC-3 load-sensitive WARN tier closing the audit 10s blind spot + pretest:integration wiring; AC-4 serial-manifest hygiene annotations + timeout-as-hang-guard principle; AC-5 docs/integration-test-coverage-audit.md.

Gate: tsc 0, eslint 0, 7 audits, test:fast 5807/0, test:integration 438/438, test:expensive 14/0.