feat: context window from model endpoints + percentage-based auto-compact

ModelInfo (kernel contract):
- Add contextWindow?: number field

OpenAI-stream listModels:
- Parse contextWindow from common field names (context_length,
  context_window, max_context_length, max_tokens)

Transport-contract:
- ModelsResponse: add optional modelInfo map (model name → { contextWindow? })
- Add ModelMetadata type
- Rename CompactThresholdResponse → CompactPercentResponse
- Rename SetCompactThresholdRequest → SetCompactPercentRequest

Credential store:
- Add getModelInfo(modelName) method — resolves full ModelInfo
  (including contextWindow) for a <credential>/<model> string

Transport-http:
- GET /models now includes modelInfo with contextWindow per model
- Rename compact-threshold endpoints → compact-percent

Session-orchestrator:
- Auto-compact now uses contextSize (not overcounted usage.inputTokens)
  compared against contextWindow * (percent / 100)
- Default percent: 85 (was flat 350000)
- resolveModelInfo dep added to look up contextWindow
- Passes modelName from the settled turn to the compaction service

Conversation store:
- Rename getCompactThreshold/setCompactThreshold → getCompactPercent/setCompactPercent
- compactThresholdKey → compact-percent key

4 files changed, 43 insertions, 24 deletions

diff --git a/packages/transport-http/src/app.test.ts b/packages/transport-http/src/app.test.ts
index 674fd94..11f74f5 100644
--- a/packages/transport-http/src/app.test.ts
+++ b/packages/transport-http/src/app.test.ts
@@ -139,10 +139,10 @@ function createFakeConversationStore(
 		},
 		async setConversationStatus() {},
 		async replaceHistory() {},
-		async getCompactThreshold() {
+		async getCompactPercent() {
 			return null;
 		},
-		async setCompactThreshold() {},
+		async setCompactPercent() {},
 		async forkHistory() {},
 		async setCompactedFrom() {},
 	};
@@ -241,6 +241,9 @@ function createFakeCredentialStore(models: string[]): CredentialStore {
 		resolve() {
 			return undefined;
 		},
+		async getModelInfo() {
+			return undefined;
+		},
 		async listCatalog() {
 			return models;
 		},
@@ -252,6 +255,9 @@ function createThrowingCredentialStore(error: Error): CredentialStore {
 		resolve() {
 			return undefined;
 		},
+		async getModelInfo() {
+			return undefined;
+		},
 		async listCatalog() {
 			throw error;
 		},
@@ -876,10 +882,10 @@ describe("GET /conversations/:id", () => {
 				},
 				async setConversationStatus() {},
 				async replaceHistory() {},
-				async getCompactThreshold() {
+				async getCompactPercent() {
 					return null;
 				},
-				async setCompactThreshold() {},
+				async setCompactPercent() {},
 				async forkHistory() {},
 				async setCompactedFrom() {},
 			};
@@ -951,10 +957,10 @@ describe("GET /conversations/:id", () => {
 			},
 			async setConversationStatus() {},
 			async replaceHistory() {},
-			async getCompactThreshold() {
+			async getCompactPercent() {
 				return null;
 			},
-			async setCompactThreshold() {},
+			async setCompactPercent() {},
 			async forkHistory() {},
 			async setCompactedFrom() {},
 		};
@@ -1095,10 +1101,10 @@ describe("GET /conversations/:id/metrics", () => {
 			},
 			async setConversationStatus() {},
 			async replaceHistory() {},
-			async getCompactThreshold() {
+			async getCompactPercent() {
 				return null;
 			},
-			async setCompactThreshold() {},
+			async setCompactPercent() {},
 			async forkHistory() {},
 			async setCompactedFrom() {},
 		};
@@ -2072,10 +2078,10 @@ describe("PUT /conversations/:id/reasoning-effort", () => {
 			},
 			async setConversationStatus() {},
 			async replaceHistory() {},
-			async getCompactThreshold() {
+			async getCompactPercent() {
 				return null;
 			},
-			async setCompactThreshold() {},
+			async setCompactPercent() {},
 			async forkHistory() {},
 			async setCompactedFrom() {},
 		};
diff --git a/packages/transport-http/src/app.ts b/packages/transport-http/src/app.ts
index a2ee18c..f917846 100644
--- a/packages/transport-http/src/app.ts
+++ b/packages/transport-http/src/app.ts
@@ -1,8 +1,8 @@
 import type { AgentEvent, HostAPI, Logger } from "@dispatch/kernel";
 import type {
 	CloseConversationResponse,
+	CompactPercentResponse,
 	CompactResponse,
-	CompactThresholdResponse,
 	ConversationHistoryResponse,
 	ConversationListResponse,
 	ConversationMetricsResponse,
@@ -14,7 +14,7 @@ import type {
 	OpenConversationResponse,
 	QueueResponse,
 	ReasoningEffortResponse,
-	SetCompactThresholdRequest,
+	SetCompactPercentRequest,
 	ThroughputResponse,
 	TitleResponse,
 	WarmResponse,
@@ -233,7 +233,17 @@ export function createApp(opts: CreateServerOptions): Hono {
 	app.get("/models", async (c) => {
 		try {
 			const models = await opts.credentialStore.listCatalog();
-			const body: ModelsResponse = { models };
+			const modelInfo: Record<string, { contextWindow?: number }> = {};
+			for (const modelName of models) {
+				const info = await opts.credentialStore.getModelInfo(modelName);
+				if (info?.contextWindow !== undefined) {
+					modelInfo[modelName] = { contextWindow: info.contextWindow };
+				}
+			}
+			const body: ModelsResponse = {
+				models,
+				...(Object.keys(modelInfo).length > 0 ? { modelInfo } : {}),
+			};
 			return c.json(body, 200);
 		} catch (err) {
 			log.error("models: failed to retrieve catalog", { err });
@@ -739,14 +749,14 @@ export function createApp(opts: CreateServerOptions): Hono {
 		return c.json(response, 200);
 	});
 
-	app.get("/conversations/:id/compact-threshold", async (c) => {
+	app.get("/conversations/:id/compact-percent", async (c) => {
 		const conversationId = c.req.param("id");
-		const threshold = (await opts.conversationStore.getCompactThreshold(conversationId)) ?? 0;
-		const response: CompactThresholdResponse = { conversationId, threshold };
+		const threshold = (await opts.conversationStore.getCompactPercent(conversationId)) ?? 0;
+		const response: CompactPercentResponse = { conversationId, threshold };
 		return c.json(response, 200);
 	});
 
-	app.put("/conversations/:id/compact-threshold", async (c) => {
+	app.put("/conversations/:id/compact-percent", async (c) => {
 		const conversationId = c.req.param("id");
 		let body: unknown;
 		try {
@@ -754,7 +764,7 @@ export function createApp(opts: CreateServerOptions): Hono {
 		} catch {
 			return c.json({ error: "Invalid JSON body" }, 400);
 		}
-		const parsed = body as SetCompactThresholdRequest;
+		const parsed = body as SetCompactPercentRequest;
 		if (
 			typeof parsed.threshold !== "number" ||
 			!Number.isFinite(parsed.threshold) ||
@@ -763,9 +773,9 @@ export function createApp(opts: CreateServerOptions): Hono {
 			return c.json({ error: "threshold must be a non-negative number" }, 400);
 		}
 		const threshold = Math.floor(parsed.threshold);
-		await opts.conversationStore.setCompactThreshold(conversationId, threshold);
-		log.info("conversations: compact-threshold set", { conversationId, threshold });
-		const response: CompactThresholdResponse = { conversationId, threshold };
+		await opts.conversationStore.setCompactPercent(conversationId, threshold);
+		log.info("conversations: compact-percent set", { conversationId, threshold });
+		const response: CompactPercentResponse = { conversationId, threshold };
 		return c.json(response, 200);
 	});
 
diff --git a/packages/transport-http/src/extension.ts b/packages/transport-http/src/extension.ts
index f7af615..36314e6 100644
--- a/packages/transport-http/src/extension.ts
+++ b/packages/transport-http/src/extension.ts
@@ -32,7 +32,7 @@ export const manifest: Manifest = {
 			"/conversations/:id",
 			"/conversations/:id/close",
 			"/conversations/:id/compact",
-			"/conversations/:id/compact-threshold",
+			"/conversations/:id/compact-percent",
 			"/conversations/:id/cwd",
 			"/conversations/:id/last",
 			"/conversations/:id/lsp",
diff --git a/packages/transport-http/src/server.bun.test.ts b/packages/transport-http/src/server.bun.test.ts
index fa519af..86ae6bc 100644
--- a/packages/transport-http/src/server.bun.test.ts
+++ b/packages/transport-http/src/server.bun.test.ts
@@ -66,10 +66,10 @@ function fakeConversationStore(): ConversationStore {
 		},
 		async setConversationStatus() {},
 		async replaceHistory() {},
-		async getCompactThreshold() {
+		async getCompactPercent() {
 			return null;
 		},
-		async setCompactThreshold() {},
+		async setCompactPercent() {},
 		async forkHistory() {},
 		async setCompactedFrom() {},
 	};
@@ -104,6 +104,9 @@ function fakeCredentialStore(): CredentialStore {
 		resolve() {
 			return undefined;
 		},
+		async getModelInfo() {
+			return undefined;
+		},
 		async listCatalog() {
 			return [];
 		},