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, 9 insertions, 0 deletions

diff --git a/packages/kernel/src/contracts/tool.ts b/packages/kernel/src/contracts/tool.ts
index f74ce77..0699d05 100644
--- a/packages/kernel/src/contracts/tool.ts
+++ b/packages/kernel/src/contracts/tool.ts
@@ -7,6 +7,8 @@
  * Extensions may use zod internally and convert to this shape.
  */
 
+import type { Logger } from "./logging.js";
+
 /**
  * Structural JSON Schema subset for tool parameter declarations.
  * The kernel does not validate against this — the provider serializes it for
@@ -53,6 +55,13 @@ export interface ToolExecuteContext {
 	 * can clean up rather than leak.
 	 */
 	readonly signal: AbortSignal;
+
+	/**
+	 * Pre-bound Logger scoped to this tool-call span. Tools log correlated
+	 * without a global (P3). The kernel stamps extensionId, conversationId,
+	 * turnId, and spanId automatically.
+	 */
+	readonly log: Logger;
 }
 
 /**