M3b plan: every task's git add includes Cargo.lock

Task 04 added dependencies to toolkit and its git add line left out the lock
file, so the driver stopped on an unclean tree. The lock change is folded into
task 04's commit.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/plans/M3b/12-brokerd-egress.md

@@ -77,7 +77,7 @@ proxy's run, the tool's run, `kill <name>`, `rm -f <name>`, then `rm -f <name>-e
   Expected: 6 and 11 passed. Run them ten times; they must pass every time.
 - [ ] **5. Walk the exits.** For each of the four steps, say how the guard cleans up after it.
 - [ ] **6. Run the gate.** `make gate`. Expected last line: `gate: ok`.
-- [ ] **7. Log and commit.** `git add crates/brokerd docs/implementer-log.md && git commit`
+- [ ] **7. Log and commit.** `git add crates/brokerd docs/implementer-log.md Cargo.lock && git commit`
 
 ## Done when