feat(security): secret-scanner, commit-guard, llm-redaction, audit-log

- lib/secrets.ts: shared SECRET_PATTERNS + scanSecrets/redact (AWS/GitLab/GitHub/Slack tokens, private keys, JWT, generic credentials)
- lib/audit.ts: local JSONL audit (~/.config/pi-kit/audit.jsonl, 600), optional PI_KIT_AUDIT_URL POST; never logs secret values
- secret-scanner: block write/edit whose content matches a secret (complements protected-paths)
- commit-guard: enforce Conventional Commits on 'git commit -m' + scan message for secrets
- llm-redaction: redact secrets from outbound payload via before_provider_request
- audit-log: session_start + slash-command usage; wires company.json auditEndpoint into env
- config: auditEndpoint (null); package.json: npm test; test/guardrails.test.ts (16 cases, all pass)

Verified: all extensions load via pi (lib/ not loaded as extensions); npm test green.

extensions/audit-log.ts

@@ -0,0 +1,51 @@
+/**
+ * Audit Log Extension
+ *
+ * WHAT: Records session starts and slash-command usage to the local audit log
+ *       (~/.config/pi-kit/audit.jsonl). Guardrail blocks are recorded by the
+ *       guardrail extensions themselves via the shared audit() helper. If an
+ *       audit endpoint is configured it is forwarded best-effort (see below).
+ *
+ * CONFIGURE: set `auditEndpoint` in config/company.json, or the PI_KIT_AUDIT_URL
+ *       env var, to forward events. Turn everything off with PI_KIT_AUDIT_OFF=1.
+ *
+ * DISABLE: remove/rename this file from the package `extensions/` folder.
+ */
+
+import * as fs from "node:fs";
+import * as path from "node:path";
+import { fileURLToPath } from "node:url";
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
+import { audit } from "./lib/audit.ts";
+
+const HERE = path.dirname(fileURLToPath(import.meta.url));
+const CONFIG_PATH = path.join(HERE, "..", "config", "company.json");
+
+/** Wire company.json `auditEndpoint` into the env var read by audit() (unless already set). */
+function initEndpointFromConfig(): void {
+	if (process.env.PI_KIT_AUDIT_URL) return;
+	try {
+		const cfg = JSON.parse(fs.readFileSync(CONFIG_PATH, "utf8"));
+		if (typeof cfg.auditEndpoint === "string" && cfg.auditEndpoint) {
+			process.env.PI_KIT_AUDIT_URL = cfg.auditEndpoint;
+		}
+	} catch {
+		// No config / unreadable — local-only auditing.
+	}
+}
+
+export default function auditLogExtension(pi: ExtensionAPI) {
+	initEndpointFromConfig();
+
+	pi.on("session_start", async (event) => {
+		audit({ kind: "session_start", reason: (event as { reason?: string }).reason });
+	});
+
+	// Record slash-command usage (name only, no arguments — args may contain secrets).
+	pi.on("input", async (event) => {
+		const text = (event as { text?: string }).text ?? "";
+		const m = text.match(/^\/([a-z0-9:_-]+)/i);
+		if (m) audit({ kind: "command", command: m[1] });
+		return { action: "continue" };
+	});
+}