gofmt gate in agent_gates.py with its decoys (R-1160); REPORT for the day

scripts/test_gate_decoys.py

@@ -66,6 +66,9 @@ COVERS = {
                     "inside an HTML comment (R-426)",
     "observations": "R-419 in THIS repo's REPORT.md: an Observations note SAYING it carries no marker - vs the "
                     "two genuine markers (R-426)",
+    "gofmt": "R-1160: an unformatted .go file planted under internal/ of a SCRATCH copy is convicted by name - vs the "
+             "same tree formatted (passes); with no gofmt reachable, CI passes OUT LOUD and a dev machine is "
+             "INCONCLUSIVE, never a silent pass",
     "gate-decoys": "this suite, run as a gate of agent_gates.py's full run, which CI runs on every push (R-1116): "
                    "every case above is a decoy of its own gate, and ONE case that stops convicting turns the run "
                    "red - red-proved 2026-10-17 by flipping a reuse-refs FACT case to expect rc 0",
@@ -291,6 +294,32 @@ def release_cases(base, ws):
 
 
 # ── the shared felhom.eu scripts, against THIS repo's inputs ─────────────────────────────────────
+def gofmt_cases(ws):
+    """R-1160: the gofmt gate in a scratch root (its ROOT is its own grandparent directory), never the real tree."""
+    root = os.path.join(ws, "gofmt-root")
+    os.makedirs(os.path.join(root, "scripts"))
+    os.makedirs(os.path.join(root, "internal", "x"))
+    shutil.copy(os.path.join(ROOT, "scripts", "gofmt_gate.py"), os.path.join(root, "scripts", "gofmt_gate.py"))
+    gate = os.path.join(root, "scripts", "gofmt_gate.py")
+    planted = os.path.join(root, "internal", "x", "zz_gofmt_decoy.go")
+    io.open(planted, "w", encoding="utf-8").write(u"package x\n\nfunc  F( )  int {return 1}\n")
+    if shutil.which("gofmt") or shutil.which("go"):
+        rc, out = run([sys.executable, gate], root)
+        report("gofmt: FACT: an unformatted file under internal/", rc, out, 1, ("zz_gofmt_decoy.go", "GOFMT GATE FAILED"))
+        io.open(planted, "w", encoding="utf-8").write(u"package x\n\nfunc F() int { return 1 }\n")
+        rc, out = run([sys.executable, gate], root)
+        report("gofmt: GENUINE: the same file formatted", rc, out, 0, ("gofmt gate OK",))
+    else:
+        print("  --  gofmt: not runnable here (no Go toolchain) - the two cases below pin that mode")
+    for ci, want_rc, want, name in ((True, 0, "NOT CHECKED in CI", "gofmt: CI without Go"),
+                                    (False, 2, "INCONCLUSIVE", "gofmt: dev without Go")):
+        env = {"PATH": os.path.join(ws, "empty-path"), "HOME": ws}
+        if ci:
+            env["GITEA_ACTIONS"] = "true"
+        rc, out = run([sys.executable, gate], root, env=env)
+        report(name, rc, out, want_rc, (want,))
+
+
 def shared_cases(ws):
     """A scratch WORKSPACE: a clone of this repo beside symlinks to the siblings, because the shared
     scripts reach across (REUSE.md cites hub paths; instructions_gate reads the workspace CLAUDE.md)."""
@@ -353,6 +382,7 @@ def main():
         published_cases(base)
         release_cases(base, ws)
         shared_cases(ws)
+        gofmt_cases(ws)
     finally:
         srv.shutdown()
         srv.server_close()