refactor(telemetry): ship the redact waterfall without built-in rules

The seam keeps the telemetry/redact scrubbing interface but ships no rules
of its own: the innermost next() passes records through unchanged, and
deployments mount their rules as waterfall listeners. As an SDK we cannot
know which patterns are secrets in a given deployment; a shipped list
invites false confidence while catching only known shapes, and false
positives would corrupt exported bodies. Mechanism stays with the seam,
policy moves to the deployment; both READMEs and the Agent Note state the
raw-export default plainly.

The loader-composition e2e now mounts a deployment-style rule fixture and
pins the same wire behavior: secret absent, placeholder present, canonical
log untouched.

examples/headless-agent/tests/fixtures/telemetry-otel.cordis.yml

@@ -1,8 +1,13 @@
 # Test-only composition: session-telemetry-otel through the real Loader/app
 # path, exporting to the mock OTLP collector the driver starts (url via env).
+# The redact-rule entry models a deployment mounting its own scrub rule on the
+# telemetry/redact waterfall — the seam itself ships no rules.
 - id: cli-mock-llm
   name: './cli-mock-llm.ts'
 
+- id: telemetry-redact-rule
+  name: './telemetry-redact-rule.ts'
+
 - id: bash
   name: '@deepseek-ai/dsh-bash-local'
 

examples/headless-agent/tests/fixtures/telemetry-redact-rule.ts

@@ -0,0 +1,29 @@
+import type { Context } from 'cordis'
+
+/**
+ * Deployment-style redaction rule for the telemetry e2e: scrubs the fixture
+ * credential from body strings, exactly as a real deployment would mount its
+ * own rules on the `telemetry/redact` waterfall.
+ */
+
+const SECRET = /sk-e2efixture[0-9]+/g
+const PLACEHOLDER = '[E2E-REDACTED]'
+
+function scrub(value: unknown): unknown {
+  if (typeof value === 'string') return value.replace(SECRET, PLACEHOLDER)
+  if (Array.isArray(value)) return value.map(scrub)
+  if (value !== null && typeof value === 'object') {
+    return Object.fromEntries(Object.entries(value).map(([key, entry]) => [key, scrub(entry)]))
+  }
+  return value
+}
+
+export const name = 'telemetry-redact-rule'
+
+/** Mount the fixture scrub rule onto the redact waterfall. */
+export function apply(ctx: Context): void {
+  ctx.on('telemetry/redact', (_record, next) => {
+    const record = next()
+    return { ...record, body: scrub(record.body) }
+  })
+}