refactor(observability): pure-types contracts/logging + Span body channel; verbatim before/after -> LogRecord.body (273 tests)

contracts/logging.ts reduced to pure types; createLogger (+ helpers) moved to kernel/src/logging/ — @dispatch/kernel still exports it (host-bin/tool-read-file unaffected).

Span body channel (Option A): Logger.span / Span.child / Span.end accept an optional body string -> SpanOpenRecord.body / SpanCloseRecord.body. Large verbatim payloads now use body, not stringified attributes (store-fat-serve-thin; attributes stay thin/queryable for D9).

before: run-turn emits a 'prompt' span with the verbatim messages+tools in body (small scalars in attrs). after: provider.request span carries the verbatim request in body; attrs thin, auth self-redacted.

Verified: tsc -b clean, 273 tests, biome 0 warnings/0 infos. Live boot: prompt + provider.request bodies present and correlated (shared turnId); request.body no longer in attributes; auth-key leak count = 0.

2 files changed, 114 insertions, 1 deletions

diff --git a/packages/kernel/src/host/host.test.ts b/packages/kernel/src/host/host.test.ts
index 7688366..430447c 100644
--- a/packages/kernel/src/host/host.test.ts
+++ b/packages/kernel/src/host/host.test.ts
@@ -956,5 +956,118 @@ describe("createHost", () => {
 				expect(spanCloses[0].attributes?.result).toBe("ok");
 			}
 		});
+
+		it("span() with body emits body on span-open record", async () => {
+			let extLogger: Logger | undefined;
+
+			const ext = createExtension("ext", {
+				activate: (host) => {
+					extLogger = host.logger;
+				},
+			});
+
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const span = extLogger?.span("with-body", { key: "value" }, '{"payload":"hello"}');
+			span?.end();
+
+			const spanOpens = logSink.records.filter((r) => r.kind === "span-open");
+			expect(spanOpens).toHaveLength(1);
+			if (spanOpens[0]?.kind === "span-open") {
+				expect(spanOpens[0].body).toBe('{"payload":"hello"}');
+			}
+		});
+
+		it("span() without body omits body field on span-open record", async () => {
+			let extLogger: Logger | undefined;
+
+			const ext = createExtension("ext", {
+				activate: (host) => {
+					extLogger = host.logger;
+				},
+			});
+
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const span = extLogger?.span("no-body");
+			span?.end();
+
+			const spanOpens = logSink.records.filter((r) => r.kind === "span-open");
+			expect(spanOpens).toHaveLength(1);
+			if (spanOpens[0]?.kind === "span-open") {
+				expect(spanOpens[0].body).toBeUndefined();
+			}
+		});
+
+		it("child() with body emits body on child span-open record", async () => {
+			let extLogger: Logger | undefined;
+
+			const ext = createExtension("ext", {
+				activate: (host) => {
+					extLogger = host.logger;
+				},
+			});
+
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const span = extLogger?.span("parent");
+			const child = span?.child("child-name", { k: "v" }, '{"child":"body"}');
+			child?.end();
+			span?.end();
+
+			const spanOpens = logSink.records.filter((r) => r.kind === "span-open");
+			const childOpen = spanOpens.find((r) => r.kind === "span-open" && r.name === "child-name");
+			expect(childOpen).toBeDefined();
+			if (childOpen?.kind === "span-open") {
+				expect(childOpen.body).toBe('{"child":"body"}');
+			}
+		});
+
+		it("end() with body emits body on span-close record", async () => {
+			let extLogger: Logger | undefined;
+
+			const ext = createExtension("ext", {
+				activate: (host) => {
+					extLogger = host.logger;
+				},
+			});
+
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const span = extLogger?.span("close-body");
+			span?.end({ body: '{"result":"data"}' });
+
+			const spanCloses = logSink.records.filter((r) => r.kind === "span-close");
+			expect(spanCloses).toHaveLength(1);
+			if (spanCloses[0]?.kind === "span-close") {
+				expect(spanCloses[0].body).toBe('{"result":"data"}');
+			}
+		});
+
+		it("end() without body omits body field on span-close record", async () => {
+			let extLogger: Logger | undefined;
+
+			const ext = createExtension("ext", {
+				activate: (host) => {
+					extLogger = host.logger;
+				},
+			});
+
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const span = extLogger?.span("no-close-body");
+			span?.end();
+
+			const spanCloses = logSink.records.filter((r) => r.kind === "span-close");
+			expect(spanCloses).toHaveLength(1);
+			if (spanCloses[0]?.kind === "span-close") {
+				expect(spanCloses[0].body).toBeUndefined();
+			}
+		});
 	});
 });
diff --git a/packages/kernel/src/host/host.ts b/packages/kernel/src/host/host.ts
index c7ec7a9..2331625 100644
--- a/packages/kernel/src/host/host.ts
+++ b/packages/kernel/src/host/host.ts
@@ -19,9 +19,9 @@ import type {
 	ServiceHandle,
 } from "../contracts/hooks.js";
 import type { LogDeps, Logger, LogSink } from "../contracts/logging.js";
-import { createLogger } from "../contracts/logging.js";
 import type { ProviderContract } from "../contracts/provider.js";
 import type { ToolContract } from "../contracts/tool.js";
+import { createLogger } from "../logging/logger.js";
 import { resolveActivationOrder } from "./dag.js";
 import { isApiVersionCompatible } from "./version.js";