feat(ai,agent,coding-agent): add sessionId for provider session-based caching

- Add sessionId to StreamOptions for providers that support session-based caching
- OpenAI Codex provider uses sessionId for prompt_cache_key and routing headers
- Agent class now accepts and forwards sessionId to stream functions
- coding-agent passes session ID from SessionManager and updates on session changes
- Update ai package README with table of contents, OpenAI Codex OAuth docs, and env vars table
- Increase Codex instructions cache TTL from 15 minutes to 24 hours
- Add tests for sessionId forwarding in ai and agent packages

packages/ai/src/providers/openai-codex-responses.ts

@@ -96,6 +96,7 @@ export const streamOpenAICodexResponses: StreamFunction<"openai-codex-responses"
 				model: model.id,
 				input: messages,
 				stream: true,
+				prompt_cache_key: options?.sessionId,
 			};
 
 			if (options?.maxTokens) {
@@ -132,7 +133,7 @@ export const streamOpenAICodexResponses: StreamFunction<"openai-codex-responses"
 			const transformedBody = await transformRequestBody(params, codexOptions, systemPrompt);
 
 			const reasoningEffort = transformedBody.reasoning?.effort ?? null;
-			const headers = createCodexHeaders(model.headers, accountId, apiKey, transformedBody.prompt_cache_key);
+			const headers = createCodexHeaders(model.headers, accountId, apiKey, options?.sessionId);
 			logCodexDebug("codex request", {
 				url,
 				model: params.model,

packages/ai/src/providers/openai-codex/prompts/codex.ts

@@ -115,7 +115,7 @@ export async function getCodexInstructions(normalizedModel = "gpt-5.1-codex"): P
 			cachedTimestamp = metadata.lastChecked;
 		}
 
-		const CACHE_TTL_MS = 15 * 60 * 1000;
+		const CACHE_TTL_MS = 24 * 60 * 60 * 1000;
 		if (cachedTimestamp && Date.now() - cachedTimestamp < CACHE_TTL_MS && existsSync(cacheFile)) {
 			return readFileSync(cacheFile, "utf8");
 		}
@@ -183,45 +183,3 @@ export async function getCodexInstructions(normalizedModel = "gpt-5.1-codex"): P
 		throw new Error(`No cached Codex instructions available for ${modelFamily}`);
 	}
 }
-
-export const TOOL_REMAP_MESSAGE = `<user_instructions priority="0">
-<environment_override priority="0">
-YOU ARE IN A DIFFERENT ENVIRONMENT. These instructions override ALL previous tool references.
-</environment_override>
-
-<tool_replacements priority="0">
-<critical_rule priority="0">
-❌ APPLY_PATCH DOES NOT EXIST → ✅ USE "edit" INSTEAD
-- NEVER use: apply_patch, applyPatch
-- ALWAYS use: edit tool for ALL file modifications
-</critical_rule>
-
-<critical_rule priority="0">
-❌ UPDATE_PLAN DOES NOT EXIST
-- NEVER use: update_plan, updatePlan, read_plan, readPlan, todowrite, todoread
-- There is no plan tool in this environment
-</critical_rule>
-</tool_replacements>
-
-<available_tools priority="0">
-File Operations:
-  • read  - Read file contents
-  • edit  - Modify files with exact find/replace
-  • write - Create or overwrite files
-
-Search/Discovery:
-  • grep  - Search file contents for patterns (read-only)
-  • find  - Find files by glob pattern (read-only)
-  • ls    - List directory contents (read-only)
-
-Execution:
-  • bash  - Run shell commands
-</available_tools>
-
-<verification_checklist priority="0">
-Before file modifications:
-1. Am I using "edit" NOT "apply_patch"?
-2. Am I avoiding plan tools entirely?
-3. Am I using only the tools listed above?
-</verification_checklist>
-</user_instructions>`;

packages/ai/src/providers/openai-codex/request-transformer.ts

@@ -35,6 +35,7 @@ export interface RequestBody {
 	};
 	include?: string[];
 	prompt_cache_key?: string;
+	prompt_cache_retention?: "in_memory" | "24h";
 	max_output_tokens?: number;
 	max_completion_tokens?: number;
 	[key: string]: unknown;

packages/ai/src/stream.ts

@@ -177,6 +177,7 @@ function mapOptionsForApi<TApi extends Api>(
 		maxTokens: options?.maxTokens || Math.min(model.maxTokens, 32000),
 		signal: options?.signal,
 		apiKey: apiKey || options?.apiKey,
+		sessionId: options?.sessionId,
 	};
 
 	// Helper to clamp xhigh to high for providers that don't support it

packages/ai/src/types.ts

@@ -64,6 +64,12 @@ export interface StreamOptions {
 	maxTokens?: number;
 	signal?: AbortSignal;
 	apiKey?: string;
+	/**
+	 * Optional session identifier for providers that support session-based caching.
+	 * Providers can use this to enable prompt caching, request routing, or other
+	 * session-aware features. Ignored by providers that don't support it.
+	 */
+	sessionId?: string;
 }
 
 // Unified options with reasoning passed to streamSimple() and completeSimple()