fix(bridge): toWireRecord no longer assigns undefined to session_id/phase/plugin

Caught by live-cockpit audit: 6 of 7 continuous-loop scenarios
(emu/lich/naga/gorgon synthetic events, djinn.drift.observed, runtime.metrics,
plus pech.ledger.appended via the loop) were silently swallowed at the
TS-side schema-validate-before-emit gate.

Root cause: toWireRecord checks
    if (record.session_id === undefined && event.session_id !== '')
to copy session_id off the envelope. When event.session_id is undefined
(no explicit publisher-supplied id), the comparison
    undefined !== ''
evaluates TRUE, so the line writes
    record.session_id = undefined
into the in-memory record. JSON.stringify drops undefined on the wire,
BUT validateEvent runs against the in-memory record BEFORE
serialization and rejects with "expected type string, got undefined
at /session_id" — bridge logs warning and drops event.

Fix: tighten all three convenience-copy guards to require a NON-EMPTY
STRING source value before assignment. Same pattern applied to
phase + plugin for symmetry. Direct probe verifies all 8 representative
synthetic event types now make it onto stdout where 0 did before.

No new top-level deps. TS tests still 394/0.

Author: klaiderman

src/observability/bridge.ts

@@ -66,13 +66,26 @@ export function toWireRecord(event: EnchantedEvent): Record<string, unknown> {
   // Convenience: copy session_id / phase / plugin off the envelope when the
   // payload didn't already provide them. Rust's GenericPayload reads these
   // off the top level, and well-typed variants accept them too.
-  if (record.session_id === undefined && event.session_id !== '') {
+  //
+  // CRITICAL: only set the field when the source value is a non-empty
+  // STRING. An `undefined` value here was historically writing
+  // `record.session_id = undefined`, which JSON.stringify drops on the
+  // wire — but the schema validator runs on the IN-MEMORY record BEFORE
+  // serialization and rejects with "expected string, got undefined",
+  // silently dropping any synthetic event whose publisher didn't set
+  // session_id. (Caught by the live-cockpit audit: 6 of 7 loop scenarios
+  // had every event swallowed at this boundary.)
+  if (
+    record.session_id === undefined &&
+    typeof event.session_id === 'string' &&
+    event.session_id !== ''
+  ) {
     record.session_id = event.session_id;
   }
-  if (record.phase === undefined && event.phase !== undefined) {
+  if (record.phase === undefined && typeof event.phase === 'string' && event.phase !== '') {
     record.phase = event.phase;
   }
-  if (record.plugin === undefined && event.source !== '') {
+  if (record.plugin === undefined && typeof event.source === 'string' && event.source !== '') {
     record.plugin = event.source;
   }