Read hook payload from fd 0, not /dev/stdin

Claude Code delivers the hook payload on a socket. Opening it by path
('/dev/stdin' -> /proc/self/fd/0) fails with ENXIO, so bash-guard.mjs threw on
every invocation and its bare catch exited 0 silently. The guard looked like it
was never dispatched; it was dying on line 29 each time.

readFileSync(0) is read() on the descriptor with no open(), which works on a
socket. The catch now logs instead of swallowing, so this failure mode can never
again masquerade as non-dispatch.

Adds test-bash-guard.py, which drives the guard over a socketpair. A pipe would
not reproduce the bug, so the socket is load-bearing. Verified failing against
the pre-fix guard (silent, no output) and passing after.

Removes the five diagnostic probes and probe.mjs; they served their purpose.
Bumps to 1.0.2 because the plugin cache is keyed by version and an unchanged
version silently skips reinstall.

plugins/guards/hooks/bash-guard.mjs

@@ -24,10 +24,17 @@ const deny = (reason) => {
   process.exit(0);
 };
 
+// Read fd 0 directly. Claude Code delivers the payload on a socket, and opening it by path
+// ('/dev/stdin' -> /proc/self/fd/0) fails ENXIO. readFileSync(0) is read() with no open().
 let input;
 try {
-  input = JSON.parse(readFileSync('/dev/stdin', 'utf8'));
-} catch {
+  input = JSON.parse(readFileSync(0, 'utf8'));
+} catch (e) {
+  // Never swallow this silently: a guard that dies here is indistinguishable from one that
+  // never ran, which is exactly what hid the ENXIO bug for three sessions.
+  try {
+    appendFileSync('/tmp/bash-guard-mode.log', `stdin-FAILED err=${e?.message ?? e}\n`);
+  } catch {}
   process.exit(0);
 }
 const command = input?.tool_input?.command ?? '';