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).

2 files changed, 23 insertions, 8 deletions

diff --git a/packages/kernel/src/bus/bus.test.ts b/packages/kernel/src/bus/bus.test.ts
index 7366b50..05cf875 100644
--- a/packages/kernel/src/bus/bus.test.ts
+++ b/packages/kernel/src/bus/bus.test.ts
@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, it } from "vitest";
-import type { Logger } from "../contracts/extension.js";
 import { defineEventHook, defineFilter, defineService } from "../contracts/hooks.js";
+import type { Logger, Span } from "../contracts/logging.js";
 import { type Bus, createBus } from "./bus.js";
 import { applyFilterChain, dispatchEventSync, sortFilters } from "./pure.js";
 
@@ -10,15 +10,30 @@ interface FakeLogger extends Logger {
 
 function createFakeLogger(): FakeLogger {
 	const errors: Array<{ message: string; args: unknown[] }> = [];
-	return {
+	const logger: FakeLogger = {
 		errors,
 		debug: () => {},
 		info: () => {},
 		warn: () => {},
-		error: (message: string, ...args: unknown[]) => {
-			errors.push({ message, args });
+		error: (message, attrs) => {
+			errors.push({ message, args: attrs === undefined ? [] : [attrs] });
 		},
+		child: () => logger,
+		span: () => makeNoopSpan(logger),
 	};
+	return logger;
+}
+
+function makeNoopSpan(log: Logger): Span {
+	const span: Span = {
+		id: "noop",
+		log,
+		setAttributes: () => {},
+		addLink: () => {},
+		child: () => span,
+		end: () => {},
+	};
+	return span;
 }
 
 describe("event hooks", () => {
diff --git a/packages/kernel/src/bus/pure.ts b/packages/kernel/src/bus/pure.ts
index 7cd9143..4d90fc6 100644
--- a/packages/kernel/src/bus/pure.ts
+++ b/packages/kernel/src/bus/pure.ts
@@ -12,11 +12,11 @@ export function dispatchEventSync<T>(
 			const result = handler(payload);
 			if (result instanceof Promise) {
 				result.catch((err: unknown) => {
-					logger.error(`Event hook "${hookId}" handler rejected`, err);
+					logger.error(`Event hook "${hookId}" handler rejected`, { err });
 				});
 			}
 		} catch (err) {
-			logger.error(`Event hook "${hookId}" handler threw`, err);
+			logger.error(`Event hook "${hookId}" handler threw`, { err });
 		}
 	}
 }
@@ -32,7 +32,7 @@ export async function dispatchEventAsync<T>(
 		try {
 			await handler(payload);
 		} catch (err) {
-			logger.error(`Event hook "${hookId}" handler threw`, err);
+			logger.error(`Event hook "${hookId}" handler threw`, { err });
 		}
 	});
 
@@ -76,7 +76,7 @@ export async function applyFilterChain<T>(
 			current = await fn(current);
 		} catch (err) {
 			if (failClosed) throw err;
-			logger.error(`Filter "${hookId}" handler threw (fail-open, passing through)`, err);
+			logger.error(`Filter "${hookId}" handler threw (fail-open, passing through)`, { err });
 		}
 	}
 	return current;