fix(#2832): gsd-sdk auto detects Codex runtime correctly (#2844)

* fix(#2832): gsd-sdk auto detects Codex runtime correctly

Two-part fix for #2832 (gsd-sdk auto silently routing non-Claude runtime
projects through the Claude Agent SDK):

1. Runtime gate at the `auto` entry point. New `runtime-gate.ts` exports
   `assertRuntimeSupportsAutoMode(config)` which throws an actionable error
   when `GSD_RUNTIME` / `config.runtime` resolves to a non-Claude runtime
   (codex, gemini, opencode, etc.). The autonomous orchestrator only knows
   how to drive `@anthropic-ai/claude-agent-sdk` today; failing fast with a
   clear pointer at the in-session slash commands beats the previous instant
   `[FAILED] $0.00 0.1s` flake. Wired into `cli.ts` before the GSD/InitRunner
   construction.

2. Runtime-aware `resolveModel()` in `session-runner.ts`. The profile -> id
   map (`balanced -> claude-sonnet-4-6`, etc.) was applied unconditionally,
   so even with `runtime: codex` and `resolve_model_ids: omit` the SDK
   forced a Claude id into `query()`. Now the profile map only fires when
   the runtime is Claude and the explicit `resolve_model_ids: "omit"` knob
   short-circuits to undefined, mirroring `query/config-query.ts`.

Tests (vitest, sdk/src):
- runtime-gate.test.ts (8 cases): claude / unset / unknown pass; codex,
  gemini, opencode throw; GSD_RUNTIME wins over config.runtime; error
  message references #2832 and the slash-command workaround.
- session-runner.test.ts (4 new cases under "resolveModel runtime
  awareness (#2832)"): codex runtime + balanced profile -> no model
  injected; resolve_model_ids: omit -> no model; claude runtime still
  resolves to claude-sonnet-4-6 (no regression); explicit options.model
  wins on any runtime.

* fix(#2832): address CR — env-precedence in resolveModel + accurate source attribution

Two CodeRabbit findings on PR #2844:

1. session-runner.ts:resolveModel() (Major) — read runtime via detectRuntime()
   so GSD_RUNTIME env precedence is honored. Without this, a Codex run with
   a Claude-shaped config still fell into the Claude-only profile-id branch.

2. runtime-gate.ts:assertRuntimeSupportsAutoMode() (Minor) — when GSD_RUNTIME
   holds an unsupported value, detectRuntime() falls through to config but
   the source label still reported the discarded env value. Fix: validate
   env against SUPPORTED_RUNTIMES before attributing the source.

Tests added for both: env-precedence in session-runner, source attribution
in runtime-gate. 17/17 pass.

sdk/src/session-runner.ts

@@ -13,6 +13,7 @@ import type { GSDConfig } from './config.js';
 import { buildExecutorPrompt, parseAgentTools, DEFAULT_ALLOWED_TOOLS } from './prompt-builder.js';
 import type { GSDEventStream, EventStreamContext } from './event-stream.js';
 import { getToolsForPhase } from './tool-scoping.js';
+import { detectRuntime } from './query/helpers.js';
 
 // ─── Model resolution ────────────────────────────────────────────────────────
 
@@ -20,11 +21,34 @@ import { getToolsForPhase } from './tool-scoping.js';
  * Resolve model identifier from options or config profile.
  *
  * Priority: explicit model option > config model_profile > default.
+ *
+ * Runtime-aware (#2832): the profile -> Claude-id map only applies when the
+ * project is targeting the Claude runtime. For Codex, Gemini, OpenCode, etc.,
+ * forcing a Claude model id (e.g. 'claude-sonnet-4-6') silently routes the
+ * autonomous run through the Claude path, which is wrong for those runtimes.
+ * In those cases — and whenever `resolve_model_ids: "omit"` is set — leave
+ * `model` unset so the runtime falls back to its configured default.
  */
 function resolveModel(options?: SessionOptions, config?: GSDConfig): string | undefined {
   if (options?.model) return options.model;
 
-  // Map model_profile names to model IDs
+  // Honor the explicit "don't resolve model ids" config knob (#2652, #2832).
+  // Mirrors `query/config-query.ts` resolve_model_ids === 'omit' branch.
+  if ((config as Record<string, unknown> | undefined)?.resolve_model_ids === 'omit') {
+    return undefined;
+  }
+
+  // Profile -> Claude id map. Applies only on the Claude runtime.
+  // Use `detectRuntime` so `GSD_RUNTIME` env precedence is honored — a Codex
+  // run with a Claude-shaped config must NOT be silently routed to Claude.
+  const runtime = detectRuntime({
+    runtime: (config as Record<string, unknown> | undefined)?.runtime,
+  });
+  if (runtime !== 'claude') {
+    // Non-Claude runtimes: never inject a Claude id from the profile map.
+    return undefined;
+  }
+
   if (config?.model_profile) {
     const profileMap: Record<string, string> = {
       balanced: 'claude-sonnet-4-6',