diff --git a/server/services/agentLifecycle.js b/server/services/agentLifecycle.js
index 9d067d01a6..ff5172edf7 100644
--- a/server/services/agentLifecycle.js
+++ b/server/services/agentLifecycle.js
@@ -61,6 +61,7 @@ import { composeProviderEnv } from '../lib/cliChildEnv.js';
 import { cliProviderAuthDescriptor } from '../lib/processEnv.js';
 import { PROVIDER_TYPES } from '../lib/aiToolkit/constants.js';
 import { buildCliSpawnConfig, isClaudeCliProvider, isTuiProvider, getClaudeSettingsEnv, spawnDirectly } from './agentCliSpawning.js';
+import { dropUnsupportedOllamaThinking } from './ollamaAgentContext.js';
 import { buildTuiSpawnConfig, spawnTuiAgent } from './agentTuiSpawning.js';
 import { publicReviewProviderBlock, publicReviewPostureForProfile, PUBLIC_REVIEW_NO_TOOL_POSTURE } from '../lib/providerVendors.js';
 import { PUBLIC_REVIEW_ACTIONS_EXECUTION_PROFILE } from '../lib/agentExecutionProfiles.js';
@@ -907,7 +908,7 @@ async function runAgentSpawn(task) {
     // dynamic `agent.build` config instead of mutating saved provider state.
     const taskTemperature = task.metadata?.temperature === '' ? NaN : Number(task.metadata?.temperature);
     const taskThinking = task.metadata?.thinking;
-    const runProvider = {
+    const requestedProvider = {
       ...provider,
       ...(Number.isFinite(taskTemperature) && taskTemperature >= 0 && taskTemperature <= 2
         ? { temperature: taskTemperature }
@@ -915,9 +916,19 @@ async function runAgentSpawn(task) {
       ...([true, false, 'true', 'false'].includes(taskThinking) ? { thinking: taskThinking } : {}),
       ...(typeof task.metadata?.effort === 'string' ? { effort: task.metadata.effort } : {}),
     };
-    // Per-task reasoning-effort override (task form / schedule config). The
-    // builders no-op it for providers without an effort control.
-    const taskEffort = task.metadata?.effort || null;
+    // Ollama 400s the whole request when a model that never implements thinking
+    // is asked to think, so a non-reasoning local model dispatched at any effort
+    // level dies on its first turn with exit 1 and no output. Resolved here,
+    // once, on the provider EVERY spawn path shares — so the two carriers of the
+    // level (the `--effort` argv and OpenCode's `agent.*.reasoningEffort` config)
+    // drop it together. `taskEffort` is the per-task reasoning-effort override
+    // (task form / schedule config); the builders no-op it for providers without
+    // an effort control.
+    const { provider: runProvider, effort: taskEffort } = await dropUnsupportedOllamaThinking(
+      requestedProvider,
+      selectedModel,
+      task.metadata?.effort || null,
+    );
     // Codex counts the root orchestrator against its per-session thread cap.
     // Lift that cap to root + configured workers for cloud swarms so a six-way
     // claim run can actually fan out six issue agents. Never lift it for a
diff --git a/server/services/ollamaAgentContext.js b/server/services/ollamaAgentContext.js
index b14efbd40e..4c219b73c6 100644
--- a/server/services/ollamaAgentContext.js
+++ b/server/services/ollamaAgentContext.js
@@ -13,6 +13,11 @@
  * VRAM-based auto-pick stands — but a too-small window is warned about up
  * front, because the alternative is a run that dies an hour in with
  * `exceed_context_size_error`.
+ *
+ * The same "prepare the daemon before the harness starts" role covers the
+ * model's reasoning capability: Ollama rejects a whole request when a model
+ * that never implements thinking is asked to think, so
+ * `dropUnsupportedOllamaThinking` resolves that ahead of the spawn too.
  */
 
 import { isOllamaBackedProvider } from './providers.js'
@@ -26,7 +31,7 @@ import {
   isSameOllamaDaemon,
   resolveOllamaContextLength
 } from '../lib/ollamaContext.js'
-import { ensureContextWindow, getBaseUrl, getRuntimeContextLength } from './ollamaManager.js'
+import { ensureContextWindow, getBaseUrl, getModelCapabilities, getRuntimeContextLength } from './ollamaManager.js'
 
 /**
  * Prepare the Ollama daemon for an agent harness run.
@@ -77,3 +82,64 @@ export async function ensureOllamaAgentContext(provider, { env = process.env, mo
   if (warning) console.warn(warning)
   return { skipped: false, contextLength, applied: !!result.applied, warning }
 }
+
+/**
+ * Does this run's Ollama model reject a thinking request?
+ *
+ * `true` only when we KNOW it does — the daemon answered `/api/show` with a
+ * capability list that omits `thinking`. A failed probe (`null`) and an empty
+ * list both mean *unknown*, not *unsupported*, so they leave the controls
+ * alone rather than silently dropping a level the model does accept. Mirrors
+ * `modelRejectsThinking` in `codeReview.js`, which solves the same problem for
+ * the local code reviewer's own HTTP calls.
+ *
+ * A provider pointed at a REMOTE daemon is never probed: `ollamaManager` only
+ * inspects the local one, so its answer would describe the wrong host.
+ *
+ * @param {object|null} provider
+ * @param {string|null} model
+ * @returns {Promise<boolean>}
+ */
+export async function ollamaModelRejectsThinking(provider, model) {
+  if (!model || !provider || !isOllamaBackedProvider(provider)) return false
+  if (!isSameOllamaDaemon(ollamaBaseFromProvider(provider), getBaseUrl())) return false
+  const capabilities = await getModelCapabilities(model).catch(() => null)
+  if (!Array.isArray(capabilities) || capabilities.length === 0) return false
+  return !capabilities.includes('thinking')
+}
+
+/**
+ * Drop a run's reasoning controls when its Ollama model cannot think.
+ *
+ * Ollama rejects the WHOLE request rather than ignoring a field a model has no
+ * answer for — `"<model>" does not support thinking`, both on native
+ * `/api/chat` (`think: true`) and through the OpenAI-compatible
+ * `reasoning_effort` an OpenCode `agent.*.reasoningEffort` becomes. So an
+ * agent dispatched at `effort: medium` onto a non-reasoning local model
+ * (gemma3, most plain chat models) dies on its first turn with exit 1 and no
+ * output, which is how a `pr-reviewer` stage pinned to `gemma3:27b` failed
+ * three times over. The level carries no information for such a model, so
+ * dropping it loses nothing; keeping it loses the run.
+ *
+ * Resolved once per spawn, on the provider every path shares, so the two
+ * carriers of the level — the `--effort` argv and OpenCode's config block —
+ * cannot disagree. `thinking: false` is preserved: that is a request NOT to
+ * think, which every model accepts.
+ *
+ * @param {object|null} provider - the run's provider, task overrides already merged
+ * @param {string|null} model - the model this run was dispatched with
+ * @param {string|null} [effort] - the run's effort level, as passed to the argv builders
+ * @returns {Promise<{provider: object|null, effort: string|null, dropped: boolean}>}
+ */
+export async function dropUnsupportedOllamaThinking(provider, model, effort = null) {
+  const keep = { provider, effort, dropped: false }
+  const wantsThinking = !!effort
+    || (typeof provider?.effort === 'string' && provider.effort.trim() !== '')
+    || provider?.thinking === true || provider?.thinking === 'true'
+  if (!wantsThinking) return keep
+  if (!await ollamaModelRejectsThinking(provider, model)) return keep
+
+  const { effort: _requestedEffort, thinking: _requestedThinking, ...rest } = provider
+  console.warn(`⚠️ ${model} does not support thinking — running without a reasoning effort`)
+  return { provider: { ...rest, thinking: false }, effort: null, dropped: true }
+}
diff --git a/server/services/ollamaAgentContext.test.js b/server/services/ollamaAgentContext.test.js
index ccab857f8a..79d39d055d 100644
--- a/server/services/ollamaAgentContext.test.js
+++ b/server/services/ollamaAgentContext.test.js
@@ -3,11 +3,12 @@ import { describe, it, expect, vi, beforeEach } from 'vitest'
 vi.mock('./ollamaManager.js', () => ({
   ensureContextWindow: vi.fn(),
   getRuntimeContextLength: vi.fn(),
+  getModelCapabilities: vi.fn(),
   getBaseUrl: vi.fn(() => 'http://localhost:11434')
 }))
 
-import { ensureContextWindow, getRuntimeContextLength } from './ollamaManager.js'
-import { ensureOllamaAgentContext } from './ollamaAgentContext.js'
+import { ensureContextWindow, getModelCapabilities, getRuntimeContextLength } from './ollamaManager.js'
+import { dropUnsupportedOllamaThinking, ensureOllamaAgentContext } from './ollamaAgentContext.js'
 
 const claudeOllamaTui = {
   id: 'claude-ollama-tui',
@@ -89,3 +90,69 @@ describe('ensureOllamaAgentContext', () => {
     expect(ensureContextWindow).toHaveBeenCalledWith(65536)
   })
 })
+
+// Regression: a `pr-reviewer` stage dispatched at `effort: medium` onto
+// `gemma3:27b` (capabilities `["completion","vision"]`) failed three times with
+// `Error: "gemma3:27b" does not support thinking` — Ollama rejects the whole
+// request rather than ignoring the level.
+describe('dropUnsupportedOllamaThinking', () => {
+  const opencodeOllama = { id: 'opencode-ollama-tui', type: 'tui', command: 'opencode', ollamaBacked: true }
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+    vi.spyOn(console, 'warn').mockImplementation(() => {})
+  })
+
+  it('drops the effort when the model reports no thinking capability', async () => {
+    getModelCapabilities.mockResolvedValue(['completion', 'vision'])
+    const result = await dropUnsupportedOllamaThinking({ ...opencodeOllama, effort: 'medium' }, 'gemma3:27b', 'medium')
+    expect(result.dropped).toBe(true)
+    expect(result.effort).toBeNull()
+    expect(result.provider.effort).toBeUndefined()
+    expect(result.provider.thinking).toBe(false)
+  })
+
+  it('drops a thinking:true override for the same model', async () => {
+    getModelCapabilities.mockResolvedValue(['completion'])
+    const result = await dropUnsupportedOllamaThinking({ ...opencodeOllama, thinking: true }, 'gemma3:27b')
+    expect(result.dropped).toBe(true)
+    expect(result.provider.thinking).toBe(false)
+  })
+
+  it('keeps the effort for a model that does report thinking', async () => {
+    getModelCapabilities.mockResolvedValue(['completion', 'tools', 'thinking'])
+    const provider = { ...opencodeOllama, effort: 'high' }
+    expect(await dropUnsupportedOllamaThinking(provider, 'qwen3-coder:30b', 'high'))
+      .toEqual({ provider, effort: 'high', dropped: false })
+  })
+
+  // A failed probe and an empty list both mean *unknown*, not *unsupported* —
+  // dropping on either would silently strip a level the model does accept.
+  it.each([[null], [[]]])('keeps the effort when capabilities are unknown (%j)', async (capabilities) => {
+    getModelCapabilities.mockResolvedValue(capabilities)
+    expect((await dropUnsupportedOllamaThinking({ ...opencodeOllama, effort: 'high' }, 'mystery:7b', 'high')).dropped).toBe(false)
+  })
+
+  it('never probes when the run asked for no thinking at all', async () => {
+    const provider = { ...opencodeOllama }
+    expect(await dropUnsupportedOllamaThinking(provider, 'gemma3:27b', null))
+      .toEqual({ provider, effort: null, dropped: false })
+    expect(getModelCapabilities).not.toHaveBeenCalled()
+  })
+
+  it('never probes for a provider that is not Ollama-backed', async () => {
+    getModelCapabilities.mockResolvedValue(['completion'])
+    const provider = { id: 'codex-cli', type: 'cli', command: 'codex', effort: 'high' }
+    expect((await dropUnsupportedOllamaThinking(provider, 'gpt-5.6', 'high')).dropped).toBe(false)
+    expect(getModelCapabilities).not.toHaveBeenCalled()
+  })
+
+  // ollamaManager only inspects the LOCAL daemon, so its capability answer
+  // would describe the wrong host.
+  it('never probes for a provider pointed at a remote Ollama host', async () => {
+    getModelCapabilities.mockResolvedValue(['completion'])
+    const provider = { ...opencodeOllama, effort: 'high', endpoint: 'http://198.51.100.7:11434/v1' }
+    expect((await dropUnsupportedOllamaThinking(provider, 'gemma3:27b', 'high')).dropped).toBe(false)
+    expect(getModelCapabilities).not.toHaveBeenCalled()
+  })
+})