Fix Module 25 command injection + lab integrity (#24–#27) (#54)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

modules/25-autonomous-agents/lab/agent_runner.py

@@ -146,6 +146,13 @@ def simulate_fix(variant: str, attempt: int) -> None:
         DEMO_SRC.write_text("def discount(price, pct):\n    return price - price * pct / 100\n")
 
 
+def simulate_cleanup() -> None:
+    """Discard the simulator's demo artifacts. These are UNTRACKED new files, so `git restore`
+    (which only touches tracked files) can't remove them — the simulator cleans up after itself."""
+    for path in (DEMO_SRC, DEMO_TEST):
+        path.unlink(missing_ok=True)
+
+
 # --------------------------------------------------------------------------------------------------
 # The endpoint every path shares: a PR PROPOSAL. Never a merge.
 # --------------------------------------------------------------------------------------------------
@@ -173,12 +180,20 @@ def propose_pr(message: str) -> None:
     print("\nThe agent stops here. It cannot merge. That is the whole safety model.")
 
 
-def reject(reason: str, gate_output: str) -> None:
+def reject(reason: str, gate_output: str, *, simulated: bool = False) -> None:
     print(gate_output)
     print("\n" + "=" * 80)
     print(f"GATE FAILED: {reason}")
-    print("No PR proposed. The branch is left as-is for you to inspect or discard:")
-    print("    git restore .            # throw the agent's change away (Module 2)")
+    print("No PR proposed.")
+    if simulated:
+        # The simulated agent's change is the UNTRACKED demo files, which `git restore` can't touch.
+        # Discard them directly so the failed attempt leaves a clean tree.
+        simulate_cleanup()
+        print("Discarded the simulated agent's demo files (agent_demo.py, test_agent_demo.py).")
+        print("(With a real agent editing tracked files, you'd discard with: git restore .  # Module 2)")
+    else:
+        print("The branch is left as-is for you to inspect or discard:")
+        print("    git restore .            # throw the agent's change away (Module 2)")
     print("=" * 80)
 
 
@@ -198,7 +213,7 @@ def cmd_issue_to_pr(issue_path: Path, simulate: str | None) -> int:
         print(gate_output)
         propose_pr(f"Agent: implement {issue_path.stem}")
         return 0
-    reject("the agent's change does not pass the gate", gate_output)
+    reject("the agent's change does not pass the gate", gate_output, simulated=bool(simulate))
     return 1