feat(observability): Phase A logging substrate — Logger/Span ABI + journal sink (250 tests)

Structured, agent-first logging captured durably to an append-only journal file.

Kernel (contracts/logging.ts): leveled/attributed Logger + Span, auto-scoped per extension (host stamps manifest.id, unspoofable), incremental span records (open/close) for crash-reconstructable traces, injected LogSink (pure record-builder). ctx.log on ToolContract; runTurn opens turn/step/tool-call spans and captures the verbatim pre-mutation prompt (the 'before') on the step span.

journal-sink (new package, bootstrap dep — not an extension): LogSink appending NDJSON to a rotating journal; pure serialize + thin fs edge; fail-safe drop, never blocks a turn. host-bin injects it via HostDeps; session-orchestrator threads host.logger (childed per turn) into runTurn.

Redaction is per-extension self-redaction (no shared helper — isolation over DRY). The out-of-process collector + SQLite store + the verbatim 'after' provider.request capture are Phase B / next (notes/observability-design.md §10/§11).

Verified: tsc -b clean, 250 tests (218→+32), biome clean. Live boot: a turn's journal holds host logs + turn/step spans (open+close) + the prompt:before record with the verbatim messages array.

Harness: ORCHESTRATOR §3 rule-scoping map; .dispatch/rules/isolation-over-dry.md; notes/observability-design.md (design D1–D10 + Phase A/B plan).

1 files changed, 8 insertions, 0 deletions

diff --git a/packages/kernel/src/contracts/runtime.ts b/packages/kernel/src/contracts/runtime.ts
index 68c0444..1e8f14f 100644
--- a/packages/kernel/src/contracts/runtime.ts
+++ b/packages/kernel/src/contracts/runtime.ts
@@ -10,6 +10,7 @@
 import type { ChatMessage } from "./conversation.js";
 import type { ToolDispatchPolicy } from "./dispatch.js";
 import type { AgentEvent } from "./events.js";
+import type { Logger } from "./logging.js";
 import type { ProviderContract, ProviderStreamOptions, Usage } from "./provider.js";
 import type { ToolContract } from "./tool.js";
 
@@ -73,6 +74,13 @@ export interface RunTurnInput {
 
 	/** Cancellation signal for the entire turn. */
 	readonly signal?: AbortSignal;
+
+	/**
+	 * Optional logger for structured span instrumentation. The runtime opens
+	 * turn/step/tool-call spans using this logger. If omitted, no spans are
+	 * emitted (backward-compatible with callers that don't yet pass a logger).
+	 */
+	readonly logger?: Logger;
 }
 
 /**