feat(telemetry): session-telemetry seam with mandatory redaction + OTel backend

Revive the reviewed session-telemetry packages from the closed
session-telemetry-otlp-rfc branch (PR #222/#231) on current master, renamed
to @deepseek-ai/dsh-session-telemetry{,-otel} (the SDK component-telemetry
package holds the dsh-telemetry name).

Delta over the branch version: every record now passes a telemetry/redact
waterfall between projection and emit() — the innermost next() applies a
non-configurable conservative credential-shape rule set, listeners stack
stricter rules, a throwing rule withholds the record fail-closed, and the
canonical log is never rewritten. This answers the export-side concern that
closed PR #222; the boundary axiom (our aspect ends at emit(); delivery is
the reporting SDK's) is unchanged, and the runtime-telemetry RFC's outbox /
readCommitted lane is recorded as deferred in the Agent Note.

Covered by seam/redact/OTel-wire unit tiers (100% per-file) and a keyless
Loader-composition e2e that boots the examples fixture against a mock OTLP
collector and pins redaction on the wire plus the untouched canonical log.

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

@@ -0,0 +1,23 @@
+# Test-only composition: session-telemetry-otel through the real Loader/app
+# path, exporting to the mock OTLP collector the driver starts (url via env).
+- id: cli-mock-llm
+  name: './cli-mock-llm.ts'
+
+- id: bash
+  name: '@deepseek-ai/dsh-bash-local'
+
+- id: telemetry-otel
+  name: '@deepseek-ai/dsh-session-telemetry-otel'
+  config:
+    exporter:
+      url: !!js process.env.DSH_TELEMETRY_E2E_URL
+
+- id: cli-agent
+  name: '@deepseek-ai/dsh-cli-demo'
+  config:
+    provider: cli-mock
+    model: cli-mock
+    persona: 'Test the session-telemetry-otel plugin.'
+    persistenceRoot: './.sessions'
+    persistenceCompression: 'none'
+    workspaceContext: false