refactor(kernel): rename tabId → conversationId across contracts + consumers (218 tests)

Step 4 of the post-MVP backlog: resolve the last vocab drift. The canonical
term for a thread of turns is `conversationId` (GLOSSARY), but `AgentEvent`
variants and `RunTurnInput` still used the legacy `tabId` from the old frontend
"tab" concept, with session-orchestrator bridging `conversationId → tabId`.

Atomic, type-driven rename across the full 10-file consumer set:
- contracts/events.ts: all 11 AgentEvent variants tabId → conversationId
- contracts/runtime.ts: RunTurnInput.tabId → conversationId
- runtime/{events,run-turn,dispatch}.ts: factory params, ctx field, locals
- session-orchestrator: drop the redundant `tabId: conversationId` bridge line
- transport-http: emit wiring; external /chat field + X-Conversation-Id header
  unchanged (already canonical) — only the emitted NDJSON event field flips
- tests (run-turn, app, logic): inputs + assertions now use conversationId

Pure rename, zero behavior change: typecheck clean, 218 tests pass (unchanged
count), biome clean, `grep tabId packages/` → zero matches. Verified live:
multi-turn curl emits conversationId-keyed NDJSON and threads history correctly.
GLOSSARY drift note removed. Closes the post-MVP backlog (Steps 1–4).

12 files changed, 138 insertions, 81 deletions

diff --git a/GLOSSARY.md b/GLOSSARY.md
index 8ead590..dade3c2 100644
--- a/GLOSSARY.md
+++ b/GLOSSARY.md
@@ -29,12 +29,9 @@
 | **provider** | An extension wrapping an LLM backend (`stream(messages, tools)`), provider-agnostic to the kernel. | — |
 | **AgentEvent** | An outward event the runtime emits during a turn (text-delta, tool-call, usage, done, etc.). Carries `conversationId` + `turnId`. | — |
 
-## Known vocabulary drift (tracked, not yet fixed)
+## Known vocabulary drift
 
-- **`tabId` in `AgentEvent`s and `runTurn` input.** The events contract
-  (`packages/kernel/src/contracts/events.ts`) and `RunTurnInput` still use
-  **`tabId`** where the canonical term is now **`conversationId`**. The
-  session-orchestrator maps `conversationId → tabId` as a bridge. This is a
-  CONTRACT change (kernel + every consumer) — to be done as a scoped fan-out via
-  `lsp references` (see HANDOFF.md), not a silent edit. Until then, `tabId` in
-  emitted events == the `conversationId`.
+- _None._ The former `tabId` drift in `AgentEvent`s and `RunTurnInput` was fully
+  resolved (renamed to `conversationId` across contracts + every consumer; see
+  tasks.md Step 4). `tabId` is retained only in the "Aliases to avoid" column
+  above so it is never reintroduced.
diff --git a/packages/kernel/src/contracts/events.ts b/packages/kernel/src/contracts/events.ts
index ce1dae4..74e23fd 100644
--- a/packages/kernel/src/contracts/events.ts
+++ b/packages/kernel/src/contracts/events.ts
@@ -25,24 +25,24 @@ export type AgentEvent =
 	| TurnDoneEvent
 	| TurnSealedEvent;
 
-/** Status change for a tab / session (e.g. idle → running). */
+/** Status change for a conversation (e.g. idle → running). */
 export interface StatusEvent {
 	readonly type: "status";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly status: string;
 }
 
 /** A turn has begun. */
 export interface TurnStartEvent {
 	readonly type: "turn-start";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 }
 
 /** Incremental text content from the model during a turn. */
 export interface TurnTextDeltaEvent {
 	readonly type: "text-delta";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly delta: string;
 }
@@ -50,7 +50,7 @@ export interface TurnTextDeltaEvent {
 /** Incremental reasoning / thinking content during a turn. */
 export interface TurnReasoningDeltaEvent {
 	readonly type: "reasoning-delta";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly delta: string;
 }
@@ -58,7 +58,7 @@ export interface TurnReasoningDeltaEvent {
 /** The model has requested a tool to be run. */
 export interface TurnToolCallEvent {
 	readonly type: "tool-call";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly toolCallId: string;
 	readonly toolName: string;
@@ -68,7 +68,7 @@ export interface TurnToolCallEvent {
 /** A tool has completed execution. */
 export interface TurnToolResultEvent {
 	readonly type: "tool-result";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly toolCallId: string;
 	readonly toolName: string;
@@ -79,7 +79,7 @@ export interface TurnToolResultEvent {
 /** Streaming output from a tool execution (e.g. shell stdout/stderr). */
 export interface TurnToolOutputEvent {
 	readonly type: "tool-output";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly toolCallId: string;
 	readonly data: string;
@@ -89,7 +89,7 @@ export interface TurnToolOutputEvent {
 /** Token usage for the current step or turn. */
 export interface TurnUsageEvent {
 	readonly type: "usage";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly usage: Usage;
 }
@@ -97,7 +97,7 @@ export interface TurnUsageEvent {
 /** An error occurred during the turn. */
 export interface TurnErrorEvent {
 	readonly type: "error";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly message: string;
 	readonly code?: string;
@@ -106,7 +106,7 @@ export interface TurnErrorEvent {
 /** The turn has completed (model finished generating). */
 export interface TurnDoneEvent {
 	readonly type: "done";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 	readonly reason: string;
 }
@@ -117,6 +117,6 @@ export interface TurnDoneEvent {
  */
 export interface TurnSealedEvent {
 	readonly type: "turn-sealed";
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 }
diff --git a/packages/kernel/src/contracts/runtime.ts b/packages/kernel/src/contracts/runtime.ts
index ff994af..68c0444 100644
--- a/packages/kernel/src/contracts/runtime.ts
+++ b/packages/kernel/src/contracts/runtime.ts
@@ -57,10 +57,10 @@ export interface RunTurnInput {
 
 	/**
 	 * Identifiers used to attribute every emitted `AgentEvent`. The kernel does
-	 * not generate these — the session-orchestrator owns turn/tab identity and
-	 * passes them in, so events are traceable to their conversation.
+	 * not generate these — the session-orchestrator owns turn/conversation identity
+	 * and passes them in, so events are traceable to their conversation.
 	 */
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 
 	/**
diff --git a/packages/kernel/src/runtime/dispatch.ts b/packages/kernel/src/runtime/dispatch.ts
index c6c5f8e..626b333 100644
--- a/packages/kernel/src/runtime/dispatch.ts
+++ b/packages/kernel/src/runtime/dispatch.ts
@@ -13,7 +13,7 @@ export async function executeToolCall(
 	tool: ToolContract | undefined,
 	signal: AbortSignal,
 	emit: EventEmitter,
-	tabId: string,
+	conversationId: string,
 	turnId: string,
 ): Promise<ToolResult> {
 	if (tool === undefined) {
@@ -26,7 +26,7 @@ export async function executeToolCall(
 		toolCallId: call.id,
 		signal,
 		onOutput: (data, stream) => {
-			emit(toolOutputEvent(tabId, turnId, call.id, data, stream));
+			emit(toolOutputEvent(conversationId, turnId, call.id, data, stream));
 		},
 	};
 	try {
@@ -48,7 +48,7 @@ export function createStepDispatcher(
 	policy: ToolDispatchPolicy,
 	signal: AbortSignal,
 	emit: EventEmitter,
-	tabId: string,
+	conversationId: string,
 	turnId: string,
 ): StepDispatcher {
 	let activeCount = 0;
@@ -78,7 +78,14 @@ export function createStepDispatcher(
 	}
 
 	async function runAndResolve(entry: QueueEntry): Promise<void> {
-		const result = await executeToolCall(entry.call, entry.tool, signal, emit, tabId, turnId);
+		const result = await executeToolCall(
+			entry.call,
+			entry.tool,
+			signal,
+			emit,
+			conversationId,
+			turnId,
+		);
 		activeCount--;
 		if (entry.tool?.concurrencySafe === false) unsafeRunning = false;
 		entry.resolve(result);
diff --git a/packages/kernel/src/runtime/events.ts b/packages/kernel/src/runtime/events.ts
index 62218be..2a92008 100644
--- a/packages/kernel/src/runtime/events.ts
+++ b/packages/kernel/src/runtime/events.ts
@@ -1,57 +1,61 @@
 import type { AgentEvent } from "../contracts/events.js";
 import type { Usage } from "../contracts/provider.js";
 
-export function textDeltaEvent(tabId: string, turnId: string, delta: string): AgentEvent {
-	return { type: "text-delta", tabId, turnId, delta };
+export function textDeltaEvent(conversationId: string, turnId: string, delta: string): AgentEvent {
+	return { type: "text-delta", conversationId, turnId, delta };
 }
 
-export function reasoningDeltaEvent(tabId: string, turnId: string, delta: string): AgentEvent {
-	return { type: "reasoning-delta", tabId, turnId, delta };
+export function reasoningDeltaEvent(
+	conversationId: string,
+	turnId: string,
+	delta: string,
+): AgentEvent {
+	return { type: "reasoning-delta", conversationId, turnId, delta };
 }
 
 export function toolCallEvent(
-	tabId: string,
+	conversationId: string,
 	turnId: string,
 	toolCallId: string,
 	toolName: string,
 	input: unknown,
 ): AgentEvent {
-	return { type: "tool-call", tabId, turnId, toolCallId, toolName, input };
+	return { type: "tool-call", conversationId, turnId, toolCallId, toolName, input };
 }
 
 export function toolResultEvent(
-	tabId: string,
+	conversationId: string,
 	turnId: string,
 	toolCallId: string,
 	toolName: string,
 	content: string,
 	isError: boolean,
 ): AgentEvent {
-	return { type: "tool-result", tabId, turnId, toolCallId, toolName, content, isError };
+	return { type: "tool-result", conversationId, turnId, toolCallId, toolName, content, isError };
 }
 
 export function toolOutputEvent(
-	tabId: string,
+	conversationId: string,
 	turnId: string,
 	toolCallId: string,
 	data: string,
 	stream: "stdout" | "stderr",
 ): AgentEvent {
-	return { type: "tool-output", tabId, turnId, toolCallId, data, stream };
+	return { type: "tool-output", conversationId, turnId, toolCallId, data, stream };
 }
 
-export function usageEvent(tabId: string, turnId: string, usage: Usage): AgentEvent {
-	return { type: "usage", tabId, turnId, usage };
+export function usageEvent(conversationId: string, turnId: string, usage: Usage): AgentEvent {
+	return { type: "usage", conversationId, turnId, usage };
 }
 
 export function errorEvent(
-	tabId: string,
+	conversationId: string,
 	turnId: string,
 	message: string,
 	code?: string,
 ): AgentEvent {
 	if (code !== undefined) {
-		return { type: "error", tabId, turnId, message, code };
+		return { type: "error", conversationId, turnId, message, code };
 	}
-	return { type: "error", tabId, turnId, message };
+	return { type: "error", conversationId, turnId, message };
 }
diff --git a/packages/kernel/src/runtime/run-turn.test.ts b/packages/kernel/src/runtime/run-turn.test.ts
index 1ea6406..696a385 100644
--- a/packages/kernel/src/runtime/run-turn.test.ts
+++ b/packages/kernel/src/runtime/run-turn.test.ts
@@ -52,7 +52,7 @@ const userMessage: ChatMessage = {
 };
 
 describe("runTurn", () => {
-	it("emits events with the tabId and turnId from input", async () => {
+	it("emits events with the conversationId and turnId from input", async () => {
 		const provider = createFakeProvider([
 			[
 				{ type: "text-delta", delta: "hi" },
@@ -68,14 +68,14 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "conv-42",
+			conversationId: "conv-42",
 			turnId: "turn-99",
 			emit,
 		});
 
 		expect(events.length).toBeGreaterThan(0);
 		for (const event of events) {
-			expect(event.tabId).toBe("conv-42");
+			expect(event.conversationId).toBe("conv-42");
 			if (event.type !== "status") {
 				expect(event.turnId).toBe("turn-99");
 			}
@@ -100,7 +100,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 		});
@@ -143,7 +143,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 		});
@@ -201,7 +201,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -250,7 +250,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [toolA, toolB],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -294,7 +294,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [toolA, toolB],
 			dispatch: { maxConcurrent: 2, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -352,7 +352,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [toolA, toolB, toolC],
 			dispatch: { maxConcurrent: 0, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -413,7 +413,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: true },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -464,7 +464,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -513,7 +513,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 			signal: ac.signal,
@@ -545,7 +545,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 			signal: ac.signal,
@@ -583,7 +583,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 		});
@@ -657,7 +657,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [unsafeTool, safeTool],
 			dispatch: { maxConcurrent: 5, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -691,7 +691,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 		});
@@ -724,7 +724,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 		});
@@ -759,7 +759,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit: () => {},
 		});
@@ -797,7 +797,7 @@ describe("runTurn", () => {
 			messages: [userMessage],
 			tools: [tool],
 			dispatch: { maxConcurrent: 1, eager: false },
-			tabId: "tab-test",
+			conversationId: "tab-test",
 			turnId: "turn-test",
 			emit,
 		});
diff --git a/packages/kernel/src/runtime/run-turn.ts b/packages/kernel/src/runtime/run-turn.ts
index 919491a..9421d86 100644
--- a/packages/kernel/src/runtime/run-turn.ts
+++ b/packages/kernel/src/runtime/run-turn.ts
@@ -74,7 +74,7 @@ interface StepContext {
 	readonly dispatch: RunTurnInput["dispatch"];
 	readonly emit: EventEmitter;
 	readonly signal: AbortSignal;
-	readonly tabId: string;
+	readonly conversationId: string;
 	readonly turnId: string;
 }
 
@@ -96,11 +96,11 @@ function processEvent(
 	switch (event.type) {
 		case "text-delta":
 			appendTextDelta(chunks, event.delta);
-			ctx.emit(textDeltaEvent(ctx.tabId, ctx.turnId, event.delta));
+			ctx.emit(textDeltaEvent(ctx.conversationId, ctx.turnId, event.delta));
 			break;
 		case "reasoning-delta":
 			appendThinkingDelta(chunks, event.delta);
-			ctx.emit(reasoningDeltaEvent(ctx.tabId, ctx.turnId, event.delta));
+			ctx.emit(reasoningDeltaEvent(ctx.conversationId, ctx.turnId, event.delta));
 			break;
 		case "tool-call": {
 			const call: ToolCall = {
@@ -115,14 +115,22 @@ function processEvent(
 				toolName: event.toolName,
 				input: event.input,
 			});
-			ctx.emit(toolCallEvent(ctx.tabId, ctx.turnId, event.toolCallId, event.toolName, event.input));
+			ctx.emit(
+				toolCallEvent(
+					ctx.conversationId,
+					ctx.turnId,
+					event.toolCallId,
+					event.toolName,
+					event.input,
+				),
+			);
 			if (ctx.dispatch.eager) {
 				dispatcher.submit(call);
 			}
 			break;
 		}
 		case "usage":
-			ctx.emit(usageEvent(ctx.tabId, ctx.turnId, event.usage));
+			ctx.emit(usageEvent(ctx.conversationId, ctx.turnId, event.usage));
 			break;
 		case "finish":
 			break;
@@ -132,7 +140,7 @@ function processEvent(
 			} else {
 				chunks.push({ type: "error", message: event.message });
 			}
-			ctx.emit(errorEvent(ctx.tabId, ctx.turnId, event.message, event.code));
+			ctx.emit(errorEvent(ctx.conversationId, ctx.turnId, event.message, event.code));
 			break;
 	}
 }
@@ -148,7 +156,7 @@ async function executeStep(ctx: StepContext): Promise<StepResult> {
 		ctx.dispatch,
 		ctx.signal,
 		ctx.emit,
-		ctx.tabId,
+		ctx.conversationId,
 		ctx.turnId,
 	);
 
@@ -167,7 +175,7 @@ async function executeStep(ctx: StepContext): Promise<StepResult> {
 	} catch (err) {
 		const message = err instanceof Error ? err.message : String(err);
 		chunks.push({ type: "error", message });
-		ctx.emit(errorEvent(ctx.tabId, ctx.turnId, message));
+		ctx.emit(errorEvent(ctx.conversationId, ctx.turnId, message));
 		finishReason = "error";
 	}
 
@@ -184,7 +192,16 @@ async function executeStep(ctx: StepContext): Promise<StepResult> {
 		const result = results.get(call.id);
 		if (result !== undefined) {
 			const isError = result.isError ?? false;
-			ctx.emit(toolResultEvent(ctx.tabId, ctx.turnId, call.id, call.name, result.content, isError));
+			ctx.emit(
+				toolResultEvent(
+					ctx.conversationId,
+					ctx.turnId,
+					call.id,
+					call.name,
+					result.content,
+					isError,
+				),
+			);
 			toolMessages.push({
 				role: "tool",
 				chunks: [
@@ -217,7 +234,7 @@ export async function runTurn(input: RunTurnInput): Promise<RunTurnResult> {
 		toolMap.set(tool.name, tool);
 	}
 
-	const tabId = input.tabId;
+	const conversationId = input.conversationId;
 	const turnId = input.turnId;
 	const signal = input.signal ?? new AbortController().signal;
 
@@ -235,7 +252,7 @@ export async function runTurn(input: RunTurnInput): Promise<RunTurnResult> {
 			dispatch: input.dispatch,
 			emit: input.emit,
 			signal,
-			tabId,
+			conversationId,
 			turnId,
 		});
 
diff --git a/packages/session-orchestrator/src/orchestrator.ts b/packages/session-orchestrator/src/orchestrator.ts
index f209d2d..302404e 100644
--- a/packages/session-orchestrator/src/orchestrator.ts
+++ b/packages/session-orchestrator/src/orchestrator.ts
@@ -48,7 +48,7 @@ export function createSessionOrchestrator(deps: SessionOrchestratorDeps): Sessio
 				tools,
 				dispatch,
 				emit: onEvent,
-				tabId: conversationId,
+				conversationId,
 				turnId,
 				...(signal !== undefined ? { signal } : {}),
 			});
diff --git a/packages/transport-http/src/app.test.ts b/packages/transport-http/src/app.test.ts
index 0125952..9763605 100644
--- a/packages/transport-http/src/app.test.ts
+++ b/packages/transport-http/src/app.test.ts
@@ -66,10 +66,10 @@ describe("POST /chat", () => {
 
 	it("streams events as NDJSON", async () => {
 		const events: AgentEvent[] = [
-			{ type: "turn-start", tabId: "tab1", turnId: "turn1" },
-			{ type: "text-delta", tabId: "tab1", turnId: "turn1", delta: "Hello" },
-			{ type: "text-delta", tabId: "tab1", turnId: "turn1", delta: " world" },
-			{ type: "done", tabId: "tab1", turnId: "turn1", reason: "stop" },
+			{ type: "turn-start", conversationId: "tab1", turnId: "turn1" },
+			{ type: "text-delta", conversationId: "tab1", turnId: "turn1", delta: "Hello" },
+			{ type: "text-delta", conversationId: "tab1", turnId: "turn1", delta: " world" },
+			{ type: "done", conversationId: "tab1", turnId: "turn1", reason: "stop" },
 		];
 		const app = createApp({ orchestrator: createFakeOrchestrator(events) });
 
@@ -98,7 +98,7 @@ describe("POST /chat", () => {
 	it("generates conversationId when not provided", async () => {
 		const app = createApp({
 			orchestrator: createFakeOrchestrator([
-				{ type: "done", tabId: "tab1", turnId: "turn1", reason: "stop" },
+				{ type: "done", conversationId: "tab1", turnId: "turn1", reason: "stop" },
 			]),
 			generateId: () => "generated-uuid",
 		});
diff --git a/packages/transport-http/src/app.ts b/packages/transport-http/src/app.ts
index 92553b7..e1e954c 100644
--- a/packages/transport-http/src/app.ts
+++ b/packages/transport-http/src/app.ts
@@ -48,7 +48,7 @@ export function createApp(opts: CreateServerOptions): Hono {
 			.catch((err) => {
 				events.push({
 					type: "error",
-					tabId: conversationId,
+					conversationId,
 					turnId: "",
 					message: err instanceof Error ? err.message : String(err),
 				});
diff --git a/packages/transport-http/src/logic.test.ts b/packages/transport-http/src/logic.test.ts
index 4a77643..a0f3fe6 100644
--- a/packages/transport-http/src/logic.test.ts
+++ b/packages/transport-http/src/logic.test.ts
@@ -79,7 +79,7 @@ describe("serializeEventLine", () => {
 	it("serializes an event as JSON followed by newline", () => {
 		const event: AgentEvent = {
 			type: "text-delta",
-			tabId: "tab1",
+			conversationId: "tab1",
 			turnId: "turn1",
 			delta: "hello",
 		};
@@ -90,7 +90,7 @@ describe("serializeEventLine", () => {
 	it("serializes a done event", () => {
 		const event: AgentEvent = {
 			type: "done",
-			tabId: "tab1",
+			conversationId: "tab1",
 			turnId: "turn1",
 			reason: "stop",
 		};
diff --git a/tasks.md b/tasks.md
index 3777b23..a212fe5 100644
--- a/tasks.md
+++ b/tasks.md
@@ -122,3 +122,35 @@ HostDeps.storageFactory). (3) host-bin wiring (orchestrator): deleted the
 now-unused `HostAPI` import. typecheck clean, **218 tests pass**, biome clean.
 Live boot: all 7 extensions activate, curl returns real responses. Summons:
 prompts/step3-{kernel-host,storage-sqlite}.md (mimo-v2.5-pro, parallel, disjoint).
+
+### Step 4 — Vocab drift: tabId → conversationId  [x] DONE (verified)
+Interlocked contract rename (every consumer breaks at once) → ONE coordinated
+multi-file owner-agent (mimo-v2.5-pro, output→reports/step4-*.run.log) owns the
+full 10-file set; orchestrator updates GLOSSARY + tasks separately.
+Files: contracts/{events,runtime}.ts, runtime/{events,run-turn,dispatch,run-turn.test}.ts,
+session-orchestrator/orchestrator.ts, transport-http/{app,app.test,logic.test}.ts.
+External `/chat` field is ALREADY conversationId — unchanged; only the internal
+field + emitted NDJSON event field flip tabId→conversationId. prompts/step4-rename-conversationid.md.
+
+**Step 4 RESULT:** done + verified. The agent renamed `tabId` → `conversationId`
+across all 10 files in one atomic change: all 11 `AgentEvent` variants
+(`contracts/events.ts`) + `RunTurnInput` (`contracts/runtime.ts`), the runtime
+event factories/`run-turn`/`dispatch`, the session-orchestrator bridge (dropped
+the redundant `tabId: conversationId` line), transport-http emit wiring, and all
+three test files (inputs + assertions). Doc comments updated ("turn/tab identity"
+→ "turn/conversation identity"; StatusEvent "tab / session" → "conversation").
+Orchestrator re-verified independently: **typecheck clean (EXIT 0)**, **218 tests
+pass** (unchanged count — pure rename, no behavior change), **biome clean**, and
+`grep tabId packages/` → **zero matches**. Agent stayed in-lane (exactly the 10
+owned files). External `/chat` request field + `X-Conversation-Id` response header
+untouched (already canonical); emitted NDJSON events now carry `conversationId`.
+GLOSSARY drift note removed. Report: reports/step4-rename-conversationid.md.
+
+---
+
+## 🏁 Post-MVP backlog COMPLETE (Steps 1–4 all done + verified)
+All four ordered HANDOFF steps landed: auth→provider seam wired, first live tool
+extension (read_file), hygiene CRs (getHostAPI + manifest honesty), and the
+tabId→conversationId vocab rename. typecheck + biome clean; 218 tests green.
+Remaining work is the parked design decisions (persistent waking agents, etc.) —
+non-blocking. See HANDOFF.md "Open design decisions still parked".