fix(custom-model): core review fixes for context-length discovery and injection

- share one context-length resolution (discovered figure, endpoint default fallback) across the routes and boot recovery, with a recovery test
- record listed per-slot context figures with a slot count of 1 and force the slot-count fallback once per rediscovery
- open up the codex model launch token for qwen3-style ids (model-plain-colon), pinned by a spawn-golden case
- pass the full discovered window to opencode as limit.context
- translate the picker search strings and document the discovery precedence

test/cli-registry-spawn-golden.test.ts

@@ -171,6 +171,15 @@ describe('codex', () => {
     expect(cx({ model: 'gpt-5', resumeSessionId: 'roll_42' })).toBe('codex --model gpt-5 resume roll_42');
   });
 
+  it('carries an Ollama-style `qwen3:32b` model id, and still drops a leading-flag shape', () => {
+    // `model-plain-colon`: the custom-model feature forces the selected id onto this param,
+    // and ids like `qwen3:32b` carry a colon. The leading-alphanumeric rule is what keeps a
+    // flag from riding the flag, so `:x` and `-x` must still drop out.
+    expect(cx({ model: 'qwen3:32b' })).toBe('codex --model qwen3:32b');
+    expect(cx({ model: ':leading' })).toBe('codex');
+    expect(cx({ model: '-yolo' })).toBe('codex');
+  });
+
   it('sends reasoning effort as one model_reasoning_effort config value, for every level', () => {
     for (const level of CODEX_REASONING_EFFORTS) {
       expect(cx({ reasoningEffort: level })).toBe(`codex --config model_reasoning_effort=${level}`);

test/custom-model-endpoint-rediscovery.test.ts

@@ -481,6 +481,52 @@ describe('refreshAllCustomModelHosts: parallel-slot enrichment (llama.cpp splits
     const [updated] = await readCustomModelHosts(dir);
     expect(updated.modelSlotCounts).toEqual({ a: 4 });
   });
+
+  it('a round where only the listed figure answers resets the slot count a loaded round learned', async () => {
+    // The false-warning scenario, measured on a real llama-swap: round 1 has the model
+    // loaded under `--ctx-size 262144 --parallel 4` — a TOTAL window shared across slots,
+    // correctly stored with its count. Round 2 finds it unloaded and takes the LISTED
+    // `context_length`, which llama-swap documents as the PER-SLOT window. If the stored 4
+    // survived, the floor check would divide the per-slot figure a second time
+    // (65536/4 = 16384) and warn about a model that serves 65536 to every request.
+    const dir = getDataDir();
+    await writeCustomModelHosts(dir, [host({ id: 'ep', baseUrl: 'http://localhost:8080' })]);
+    fetchMock.mockImplementation(async (url: URL) => {
+      if (url.pathname === '/v1/models') {
+        return new Response(JSON.stringify({ data: [{ id: 'm', status: { value: 'loaded' } }] }), { status: 200 });
+      }
+      if (url.pathname === '/running') {
+        return new Response(
+          JSON.stringify({
+            running: [{ model: 'm', state: 'ready', cmd: 'llama-server -m /models/m.gguf --ctx-size 262144 --parallel 4' }],
+          }),
+          { status: 200 }
+        );
+      }
+      throw new Error(`unexpected request: ${url.href}`); // the command answers both questions
+    });
+
+    await refreshAllCustomModelHosts();
+
+    let [round1] = await readCustomModelHosts(dir);
+    expect(round1.modelContextLengths).toEqual({ m: 262144 });
+    expect(round1.modelSlotCounts).toEqual({ m: 4 });
+
+    // Round 2: unloaded, no /running or /props probe in order, listing its per-slot figure.
+    fetchMock.mockResolvedValue(
+      new Response(JSON.stringify({ data: [{ id: 'm', status: { value: 'unloaded' }, context_length: 65536 }] }), {
+        status: 200,
+      })
+    );
+
+    await refreshAllCustomModelHosts();
+
+    const [round2] = await readCustomModelHosts(dir);
+    expect(round2.modelContextLengths).toEqual({ m: 65536 });
+    // 1 slot, not the stale 4: 65536 per slot with 1 recorded slot is the honest pair, so
+    // the floor check reads 65536/request — exactly what the server gives a single request.
+    expect(round2.modelSlotCounts).toEqual({ m: 1 });
+  });
 });
 
 describe('refreshAllCustomModelHosts: model-size enrichment (parsed from /v1/models description)', () => {

test/custom-model-injection.test.ts

@@ -112,20 +112,20 @@ describe('buildCustomModelInjection', () => {
     expect(parsed.provider.custom.models.qwen3).toEqual({});
   });
 
-  it('opencode: threads a discovered context length into the model limit with response headroom (issue #749)', () => {
+  it('opencode: threads a discovered context length into the model limit as the full window (issue #749)', () => {
     const result = buildCustomModelInjection(entryOrThrow('opencode'), endpoint, 'qwen3', 16384);
     if (result.kind !== 'env') throw new Error('unreachable');
     const parsed = JSON.parse(result.envOverrides.OPENCODE_CONFIG_CONTENT);
-    // One quarter held back for the reply: context 16384-4096, output 4096 — the sum is the
-    // real window, so a full-size prompt plus a max-length reply never exceeds the server.
-    expect(parsed.provider.custom.models.qwen3).toEqual({ limit: { context: 12288, output: 4096 } });
+    // `limit.context` IS the full window to opencode — it reserves for the reply itself —
+    // so the discovered total passes through; `output` only caps the reply at a quarter.
+    expect(parsed.provider.custom.models.qwen3).toEqual({ limit: { context: 16384, output: 4096 } });
   });
 
   it('opencode: caps the response headroom reservation at 8192 for big windows', () => {
     const result = buildCustomModelInjection(entryOrThrow('opencode'), endpoint, 'qwen3', 262144);
     if (result.kind !== 'env') throw new Error('unreachable');
     const parsed = JSON.parse(result.envOverrides.OPENCODE_CONFIG_CONTENT);
-    expect(parsed.provider.custom.models.qwen3).toEqual({ limit: { context: 253952, output: 8192 } });
+    expect(parsed.provider.custom.models.qwen3).toEqual({ limit: { context: 262144, output: 8192 } });
   });
 
   it('opencode: never invents a limit for an unknown or non-finite context length (issue #749 regression)', () => {

test/custom-model-recovery.test.ts

@@ -0,0 +1,91 @@
+/**
+ * @fileoverview Boot recovery rebuilds a saved custom-model selection through the SAME
+ * context-length resolution the routes use: the model's discovered figure, falling back to
+ * the endpoint's `defaultContextLength` (`resolveCustomModelContextLength`). Before the
+ * shared helper, `_rebuildCustomModelEnv` read `modelContextLengths` alone — so a session
+ * on a model that only the endpoint default covers came back from a Codeman restart with
+ * `CLAUDE_CODE_MAX_CONTEXT_TOKENS` (or a config file's context figure) silently gone,
+ * re-arming exactly the window overflow the var exists to prevent.
+ *
+ * `_rebuildCustomModelEnv` reads no `this` state (it re-derives everything from the endpoint
+ * store and the Session it is handed), so it is driven straight off the prototype with an
+ * empty receiver — `restoreMuxSessions()` itself cannot be reached under vitest, the same
+ * constraint recorded in test/session-model-recovery.test.ts.
+ */
+import { afterEach, describe, expect, it } from 'vitest';
+import { getDataDir } from '../src/config/instance.js';
+import { writeCustomModelHosts, type CustomModelHost } from '../src/custom-model-hosts.js';
+import { customModelConfigDir, removeConfigDir } from '../src/custom-model-injection-apply.js';
+import { Session } from '../src/session.js';
+import { WebServer } from '../src/web/server.js';
+import type { CustomModelBookkeeping } from '../src/types/session.js';
+
+type RebuildFn = (session: Session, saved: CustomModelBookkeeping) => Promise<Record<string, string> | undefined>;
+
+/** The real method, with an empty receiver — see the file header for why that is sound. */
+function rebuildCustomModelEnv(session: Session, saved: CustomModelBookkeeping) {
+  const fn = (WebServer.prototype as unknown as { _rebuildCustomModelEnv: RebuildFn })._rebuildCustomModelEnv;
+  expect(typeof fn, '_rebuildCustomModelEnv vanished from WebServer.prototype').toBe('function');
+  return fn.call({}, session, saved);
+}
+
+function endpoint(overrides: Partial<CustomModelHost> = {}): CustomModelHost {
+  return {
+    id: 'ep',
+    label: 'Ep',
+    baseUrl: 'http://localhost:8080',
+    apiKey: 'recovery-probe-key',
+    models: ['qwen3'],
+    ...overrides,
+  };
+}
+
+describe('_rebuildCustomModelEnv: context-length fallback on boot recovery', () => {
+  const configs: string[] = [];
+
+  afterEach(() => {
+    for (const id of configs.splice(0)) removeConfigDir(customModelConfigDir(id));
+  });
+
+  it('falls back to the endpoint defaultContextLength when discovery recorded no per-model figure', async () => {
+    await writeCustomModelHosts(getDataDir(), [endpoint({ defaultContextLength: 32768 })]);
+    const session = new Session({ workingDir: '/tmp', mode: 'claude' });
+    configs.push(session.id);
+
+    const env = await rebuildCustomModelEnv(session, { endpointId: 'ep', modelId: 'qwen3', envKeys: [] });
+
+    expect(env?.CLAUDE_CODE_MAX_CONTEXT_TOKENS).toBe('32768');
+  });
+
+  it('a discovered per-model figure still wins over the endpoint default', async () => {
+    await writeCustomModelHosts(getDataDir(), [
+      endpoint({ modelContextLengths: { qwen3: 131072 }, defaultContextLength: 32768 }),
+    ]);
+    const session = new Session({ workingDir: '/tmp', mode: 'claude' });
+    configs.push(session.id);
+
+    const env = await rebuildCustomModelEnv(session, { endpointId: 'ep', modelId: 'qwen3', envKeys: [] });
+
+    expect(env?.CLAUDE_CODE_MAX_CONTEXT_TOKENS).toBe('131072');
+  });
+
+  it('states nothing rather than guessing when neither source knows a window', async () => {
+    await writeCustomModelHosts(getDataDir(), [endpoint()]);
+    const session = new Session({ workingDir: '/tmp', mode: 'claude' });
+    configs.push(session.id);
+
+    const env = await rebuildCustomModelEnv(session, { endpointId: 'ep', modelId: 'qwen3', envKeys: [] });
+
+    expect(env?.CLAUDE_CODE_MAX_CONTEXT_TOKENS).toBeUndefined();
+  });
+
+  it('drops the selection to undefined (kept for clearing) when the endpoint no longer exists', async () => {
+    await writeCustomModelHosts(getDataDir(), []);
+    const session = new Session({ workingDir: '/tmp', mode: 'claude' });
+    configs.push(session.id);
+
+    await expect(rebuildCustomModelEnv(session, { endpointId: 'gone', modelId: 'qwen3', envKeys: [] })).resolves.toBe(
+      undefined
+    );
+  });
+});