diff --git a/open-sse/config/providers/registry/gemini/web/index.ts b/open-sse/config/providers/registry/gemini/web/index.ts
index 6843ae86a8..276cfaf589 100644
--- a/open-sse/config/providers/registry/gemini/web/index.ts
+++ b/open-sse/config/providers/registry/gemini/web/index.ts
@@ -8,9 +8,32 @@ export const gemini_webProvider: RegistryEntry = {
   baseUrl: "https://gemini.google.com/app",
   authType: "apikey",
   authHeader: "cookie",
+  // #9356: `supportsReasoning: false` is a live-behavior statement, not a guess
+  // about the underlying Gemini model. The executor drives the gemini.google.com
+  // web UI by typing a prompt, so it has no thinking-budget control to set and
+  // never surfaces `reasoning_content` — agent routers reading /v1/models must
+  // not select these for reasoning work. `toolCalling: false` is the matching
+  // statement for native function calling; the prompt-emulation shim (#7286)
+  // stays available and is advertised separately as `toolCalling: "emulated"`
+  // on the provider constant (src/shared/constants/providers/web-cookie.ts).
   models: [
-    { id: "gemini-3.1-pro", name: "Gemini 3.1 Pro", toolCalling: false },
-    { id: "gemini-3.5-flash", name: "Gemini 3.5 Flash", toolCalling: false },
-    { id: "gemini-3.1-flash-lite", name: "Gemini 3.1 Flash-Lite", toolCalling: false },
+    {
+      id: "gemini-3.1-pro",
+      name: "Gemini 3.1 Pro",
+      toolCalling: false,
+      supportsReasoning: false,
+    },
+    {
+      id: "gemini-3.5-flash",
+      name: "Gemini 3.5 Flash",
+      toolCalling: false,
+      supportsReasoning: false,
+    },
+    {
+      id: "gemini-3.1-flash-lite",
+      name: "Gemini 3.1 Flash-Lite",
+      toolCalling: false,
+      supportsReasoning: false,
+    },
   ],
 };
diff --git a/open-sse/executors/gemini-web.ts b/open-sse/executors/gemini-web.ts
index 975d13093f..8810b43cc3 100644
--- a/open-sse/executors/gemini-web.ts
+++ b/open-sse/executors/gemini-web.ts
@@ -14,9 +14,13 @@
  */
 
 import { BaseExecutor, type ExecuteInput } from "./base.ts";
-import { sanitizeErrorMessage } from "../utils/error.ts";
+import { buildErrorBody, sanitizeErrorMessage } from "../utils/error.ts";
 import { prepareToolMessages } from "../translator/webTools.ts";
 import { buildToolModeResponse } from "./chatgptWebTools.ts";
+import {
+  checkGeminiWebUnsupportedControls,
+  GEMINI_WEB_UNSUPPORTED_CONTROL_CODE,
+} from "./gemini-web/capabilities.ts";
 
 // ─── Constants ──────────────────────────────────────────────────────────────
 
@@ -406,6 +410,33 @@ export class GeminiWebExecutor extends BaseExecutor {
     const { model, body, stream, credentials, signal, log, onCredentialsRefreshed } = input;
     const requestBody = body as GeminiRequestBody;
 
+    // #9356: fail fast on controls this provider cannot honor (reasoning_effort
+    // above "minimal", forced tool_choice). Runs before the credential check and
+    // before Playwright launches — the request is unservable no matter which
+    // cookie is used, and answering 200 with ordinary prose made agents believe
+    // their reasoning/tool requirements had been met. See ./gemini-web/capabilities.ts.
+    const violation = checkGeminiWebUnsupportedControls(body as Record<string, unknown>);
+    if (violation) {
+      log?.warn?.(
+        "GEMINI-WEB",
+        `Rejected request: "${violation.param}" is not supported by this provider`
+      );
+      return {
+        response: new Response(
+          JSON.stringify(
+            buildErrorBody(400, violation.message, null, {
+              type: "invalid_request_error",
+              code: GEMINI_WEB_UNSUPPORTED_CONTROL_CODE,
+            })
+          ),
+          { status: 400, headers: { "Content-Type": "application/json" } }
+        ),
+        url: GEMINI_URL,
+        headers: {},
+        transformedBody: body,
+      };
+    }
+
     const cookie = resolveGeminiWebCookie(credentials);
     if (!cookie) {
       return {
diff --git a/open-sse/executors/gemini-web/capabilities.ts b/open-sse/executors/gemini-web/capabilities.ts
new file mode 100644
index 0000000000..6eefe3072f
--- /dev/null
+++ b/open-sse/executors/gemini-web/capabilities.ts
@@ -0,0 +1,121 @@
+/**
+ * Request-contract guards for the Gemini Web executor (#9356).
+ *
+ * gemini-web is not an API client. It launches Playwright, types ONE flat
+ * prompt string into the gemini.google.com `.ql-editor` contenteditable,
+ * presses Enter, and captures the first `StreamGenerate` response off the page
+ * (see ../gemini-web.ts). There is no JSON request body on the wire, which
+ * makes two OpenAI controls structurally impossible to honor:
+ *
+ *   • `reasoning_effort` — no field exists to carry a thinking budget. Unlike
+ *     deepseek-web or perplexity-web, which post a real payload and can flip a
+ *     `thinking_enabled` flag or swap the model preference, there is nothing
+ *     here to set.
+ *   • forced `tool_choice` — the tools support gemini-web does have is the
+ *     prompt-emulation shim (`translator/webTools.ts`, #7286): it ASKS the
+ *     model, in prose, to answer with `<tool>{...}</tool>` and parses whatever
+ *     comes back. That is best-effort by construction. "required" / "any" /
+ *     a named function is a GUARANTEE, and a prompt cannot make one.
+ *
+ * Before this module both were accepted and quietly ignored, so an agent got a
+ * 200 with `finish_reason: "stop"`, no `reasoning_content`, and `tool_calls: []`
+ * and concluded its requirements had been met (#9356). Failing the request is
+ * the honest answer: the caller can drop the control, or route to a model that
+ * actually implements it.
+ *
+ * Deliberately NOT rejected — these are already satisfied or already work:
+ *   • `reasoning_effort: "none" | "minimal"` — asking for as little reasoning as
+ *     possible is something a non-thinking provider trivially complies with.
+ *   • `tool_choice: "auto" | "none"` and plain `tools[]` — the #7286 emulation
+ *     path, which several shipped combos depend on (#5240, #8488). Untouched.
+ *
+ * Pure and dependency-free so the whole contract is unit-testable without a
+ * browser.
+ */
+
+/** `error.code` on every compatibility rejection raised here. */
+export const GEMINI_WEB_UNSUPPORTED_CONTROL_CODE = "unsupported_control_for_provider";
+
+/** Effort levels a non-thinking provider already complies with. */
+const SATISFIED_EFFORT_LEVELS = new Set(["none", "minimal"]);
+
+/** `tool_choice` strings that demand a tool call rather than merely offering one. */
+const FORCING_TOOL_CHOICE_STRINGS = new Set(["required", "any"]);
+
+/** `tool_choice: { type }` values that pin the model to a specific/any tool. */
+const FORCING_TOOL_CHOICE_TYPES = new Set(["function", "tool", "any"]);
+
+export interface GeminiWebCapabilityViolation {
+  /** Which request field could not be honored. */
+  param: "reasoning_effort" | "tool_choice";
+  /** Client-facing explanation — already safe to put in a response body. */
+  message: string;
+}
+
+function normalizeString(value: unknown): string | null {
+  return typeof value === "string" && value.trim().length > 0 ? value.trim().toLowerCase() : null;
+}
+
+/**
+ * True when `tool_choice` demands a tool call. Covers the OpenAI strings
+ * ("required"), the Anthropic-flavored ones the translators also emit ("any"),
+ * and the object forms that name a function or force any tool. "auto" / "none"
+ * and every unrecognized shape are treated as non-forcing — this guard only
+ * blocks contracts it is certain gemini-web cannot keep.
+ */
+export function isForcingToolChoice(toolChoice: unknown): boolean {
+  const asString = normalizeString(toolChoice);
+  if (asString) return FORCING_TOOL_CHOICE_STRINGS.has(asString);
+
+  if (toolChoice && typeof toolChoice === "object" && !Array.isArray(toolChoice)) {
+    const type = normalizeString((toolChoice as Record<string, unknown>).type);
+    return type !== null && FORCING_TOOL_CHOICE_TYPES.has(type);
+  }
+
+  return false;
+}
+
+/** True when `reasoning_effort` asks for MORE thinking than "none at all". */
+export function requestsThinkingBudget(reasoningEffort: unknown): boolean {
+  const effort = normalizeString(reasoningEffort);
+  if (effort === null) return false;
+  return !SATISFIED_EFFORT_LEVELS.has(effort);
+}
+
+/**
+ * Inspect an OpenAI-shaped request body for controls gemini-web cannot honor.
+ * Returns the first violation found, or `null` when the request is servable.
+ *
+ * `reasoning_effort` is checked before `tool_choice` only for determinism; a
+ * request carrying both is rejected either way.
+ */
+export function checkGeminiWebUnsupportedControls(
+  body: Record<string, unknown> | null | undefined
+): GeminiWebCapabilityViolation | null {
+  if (!body || typeof body !== "object") return null;
+
+  if (requestsThinkingBudget(body.reasoning_effort)) {
+    return {
+      param: "reasoning_effort",
+      message:
+        'Model provider "gemini-web" does not support "reasoning_effort". It drives the ' +
+        "gemini.google.com web UI through a typed prompt and has no thinking-budget control " +
+        'to set, so any effort above "minimal" would be silently ignored. Remove ' +
+        '"reasoning_effort" (or send "none"/"minimal") or route to a reasoning-capable model.',
+    };
+  }
+
+  if (isForcingToolChoice(body.tool_choice)) {
+    return {
+      param: "tool_choice",
+      message:
+        'Model provider "gemini-web" cannot guarantee a forced tool call. Its tool support is ' +
+        "prompt-emulated — the model is asked to emit a tool block and may answer with prose " +
+        'instead — so "tool_choice" values that require one ("required", "any", or a named ' +
+        'function) cannot be honored. Use "auto" to keep best-effort tool calling, or route to ' +
+        "a model with native function calling.",
+    };
+  }
+
+  return null;
+}
diff --git a/tests/unit/gemini-web-capabilities-9356.test.ts b/tests/unit/gemini-web-capabilities-9356.test.ts
new file mode 100644
index 0000000000..110e455c85
--- /dev/null
+++ b/tests/unit/gemini-web-capabilities-9356.test.ts
@@ -0,0 +1,258 @@
+// Capability enforcement for the Gemini Web executor (#9356).
+//
+// Reported: gemini-web silently ACCEPTS `reasoning_effort` and
+// `tool_choice: "required"` and answers with ordinary prose — HTTP 200, no
+// `reasoning_content`, `tool_calls: []`, `finish_reason: "stop"`. An
+// AgentChakra/OpenClaw agent then believes its reasoning and tool requirements
+// were honored when they were not.
+//
+// Why neither can be implemented for THIS provider: gemini-web is not an API
+// client. It launches Playwright, types a single flat prompt string into the
+// gemini.google.com `.ql-editor` contenteditable, presses Enter, and captures
+// the first `StreamGenerate` response off the page. There is no request payload
+// to carry a thinking budget, and no function-calling channel to force — the
+// tools support it does have is the prompt-emulation shim (`webTools.ts`, #7286),
+// which ASKS the model to emit `<tool>{...}</tool>` and cannot GUARANTEE it.
+//
+// So this suite pins the issue's option (b) for both controls: reject the
+// requests we cannot honor, and keep honoring the ones we can. The line drawn:
+//
+//   reasoning_effort  none | minimal        → allowed (gemini-web not thinking
+//                                             IS compliance with "spend little")
+//                     low | medium | high…  → 400, a positive request to think
+//   tool_choice       absent | auto | none  → allowed (emulation path, #7286)
+//                     required | any | {fn} → 400, a guarantee we cannot make
+//
+// The guard must run BEFORE Playwright launches, so every executor assertion
+// here completes without a browser.
+
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { GeminiWebExecutor } = await import("../../open-sse/executors/gemini-web.ts");
+const { checkGeminiWebUnsupportedControls, GEMINI_WEB_UNSUPPORTED_CONTROL_CODE } =
+  await import("../../open-sse/executors/gemini-web/capabilities.ts");
+const { gemini_webProvider } =
+  await import("../../open-sse/config/providers/registry/gemini/web/index.ts");
+const { supportsReasoning, supportsToolCalling } =
+  await import("../../src/lib/modelCapabilities.ts");
+const { providerSupportsEmulatedToolCalling } =
+  await import("../../open-sse/services/combo/comboStructure.ts");
+
+const GET_WEATHER_TOOL = {
+  type: "function",
+  function: {
+    name: "get_weather",
+    description: "Get the current weather for a city",
+    parameters: { type: "object", properties: { city: { type: "string" } }, required: ["city"] },
+  },
+};
+
+interface ErrorBodyLike {
+  error: { message: string; type: string; code: string };
+}
+
+/**
+ * Run the executor with valid-looking credentials. Every case in this suite is
+ * expected to short-circuit on the capability guard, so Playwright is never
+ * reached — a test that hangs here means the guard did not fire.
+ */
+async function run(body: Record<string, unknown>) {
+  return new GeminiWebExecutor().execute({
+    model: "gemini-3.6-flash",
+    body: { messages: [{ role: "user", content: "hi" }], stream: false, ...body },
+    stream: false,
+    credentials: { apiKey: "__Secure-1PSID=test-cookie" },
+    signal: AbortSignal.timeout(10_000),
+    log: null,
+  });
+}
+
+// ─── Pure checker: reasoning_effort ─────────────────────────────────────────
+
+test("#9356 reasoning_effort low/medium/high/xhigh are rejected as unsupported", () => {
+  for (const effort of ["low", "medium", "high", "xhigh"]) {
+    const violation = checkGeminiWebUnsupportedControls({ reasoning_effort: effort });
+    assert.equal(
+      violation?.param,
+      "reasoning_effort",
+      `reasoning_effort="${effort}" asks gemini-web to think harder, which a typed browser ` +
+        `prompt cannot express — it must be rejected, not silently dropped`
+    );
+    assert.match(violation!.message, /reasoning_effort/);
+  }
+});
+
+test("#9356 reasoning_effort none/minimal and absent stay allowed", () => {
+  assert.equal(checkGeminiWebUnsupportedControls({}), null);
+  assert.equal(checkGeminiWebUnsupportedControls({ reasoning_effort: null }), null);
+  assert.equal(checkGeminiWebUnsupportedControls({ reasoning_effort: "none" }), null);
+  assert.equal(
+    checkGeminiWebUnsupportedControls({ reasoning_effort: "minimal" }),
+    null,
+    '"minimal" means spend as little reasoning as possible — a non-thinking provider ' +
+      "already satisfies it, so rejecting it would be gratuitous"
+  );
+  assert.equal(checkGeminiWebUnsupportedControls({ reasoning_effort: "  NONE  " }), null);
+});
+
+// ─── Pure checker: tool_choice ──────────────────────────────────────────────
+
+test("#9356 tool_choice required/any is rejected as unsupported", () => {
+  for (const choice of ["required", "any"]) {
+    const violation = checkGeminiWebUnsupportedControls({
+      tools: [GET_WEATHER_TOOL],
+      tool_choice: choice,
+    });
+    assert.equal(
+      violation?.param,
+      "tool_choice",
+      `tool_choice="${choice}" is a guarantee the prompt-emulation shim cannot make`
+    );
+    assert.match(violation!.message, /tool_choice/);
+  }
+});
+
+test("#9356 a forced-function tool_choice object is rejected as unsupported", () => {
+  const violation = checkGeminiWebUnsupportedControls({
+    tools: [GET_WEATHER_TOOL],
+    tool_choice: { type: "function", function: { name: "get_weather" } },
+  });
+  assert.equal(violation?.param, "tool_choice");
+
+  // Anthropic-style forcing, which the translators also emit.
+  assert.equal(
+    checkGeminiWebUnsupportedControls({
+      tools: [GET_WEATHER_TOOL],
+      tool_choice: { type: "any" },
+    })?.param,
+    "tool_choice"
+  );
+});
+
+test("#9356 tool_choice auto/none and absent keep the #7286 emulation path open", () => {
+  assert.equal(checkGeminiWebUnsupportedControls({ tools: [GET_WEATHER_TOOL] }), null);
+  assert.equal(
+    checkGeminiWebUnsupportedControls({ tools: [GET_WEATHER_TOOL], tool_choice: "auto" }),
+    null
+  );
+  assert.equal(
+    checkGeminiWebUnsupportedControls({ tools: [GET_WEATHER_TOOL], tool_choice: "none" }),
+    null
+  );
+});
+
+test("#9356 forcing is rejected on its own terms, even with no tools[] array", () => {
+  // An agent that sets tool_choice without tools is already malformed, but the
+  // point stands: never report success for a forcing contract we ignore.
+  assert.equal(
+    checkGeminiWebUnsupportedControls({ tool_choice: "required" })?.param,
+    "tool_choice"
+  );
+});
+
+// ─── Executor wiring ────────────────────────────────────────────────────────
+
+test("#9356 executor returns 400 for reasoning_effort=high before launching a browser", async () => {
+  const result = await run({ reasoning_effort: "high" });
+
+  assert.equal(result.response.status, 400);
+  const body = (await result.response.json()) as ErrorBodyLike;
+  assert.equal(body.error.code, GEMINI_WEB_UNSUPPORTED_CONTROL_CODE);
+  assert.match(body.error.message, /reasoning_effort/);
+  assert.equal(
+    body.error.message.includes("at /"),
+    false,
+    "error bodies must stay sanitized — no stack traces"
+  );
+});
+
+test("#9356 executor returns 400 for tool_choice=required before launching a browser", async () => {
+  const result = await run({ tools: [GET_WEATHER_TOOL], tool_choice: "required" });
+
+  assert.equal(result.response.status, 400);
+  const body = (await result.response.json()) as ErrorBodyLike;
+  assert.equal(body.error.code, GEMINI_WEB_UNSUPPORTED_CONTROL_CODE);
+  assert.match(body.error.message, /tool_choice/);
+});
+
+test("#9356 the capability guard runs ahead of the credential check", async () => {
+  // A request that is BOTH uncredentialed and incompatible must report the
+  // incompatibility: adding a cookie would not make it work.
+  const result = await new GeminiWebExecutor().execute({
+    model: "gemini-3.6-flash",
+    body: { messages: [{ role: "user", content: "hi" }], reasoning_effort: "high" },
+    stream: false,
+    credentials: {},
+    signal: AbortSignal.timeout(10_000),
+    log: null,
+  });
+
+  assert.equal(result.response.status, 400);
+  const body = (await result.response.json()) as ErrorBodyLike;
+  assert.equal(body.error.code, GEMINI_WEB_UNSUPPORTED_CONTROL_CODE);
+});
+
+test("#9356 a supported request still falls through the guard untouched", async () => {
+  // tool_choice:"auto" + tools[] is the #7286 emulation contract. It must NOT
+  // be blocked — reaching the (missing) credential check proves the guard let
+  // it pass, without needing a browser to prove it.
+  const result = await new GeminiWebExecutor().execute({
+    model: "gemini-3.6-flash",
+    body: {
+      messages: [{ role: "user", content: "hi" }],
+      tools: [GET_WEATHER_TOOL],
+      tool_choice: "auto",
+    },
+    stream: false,
+    credentials: {},
+    signal: AbortSignal.timeout(10_000),
+    log: null,
+  });
+
+  assert.equal(result.response.status, 401, "should reach the cookie check, not the guard");
+});
+
+// ─── Catalog metadata ───────────────────────────────────────────────────────
+
+test("#9356 registry advertises no native tool calling and no reasoning for gemini-web", () => {
+  assert.ok(gemini_webProvider.models.length > 0);
+  for (const model of gemini_webProvider.models) {
+    assert.equal(
+      model.toolCalling,
+      false,
+      `${model.id} must not advertise native tool calling — /v1/models feeds agent routers`
+    );
+    assert.equal(
+      model.supportsReasoning,
+      false,
+      `${model.id} must advertise reasoning:false so agent routers stop selecting it for ` +
+        "reasoning work (the executor has no thinking control to drive)"
+    );
+  }
+});
+
+test("#9356 resolved capabilities — not just the raw registry — report no reasoning/tools", () => {
+  // The registry literal is only the input; `getResolvedModelCapabilities` is what
+  // the catalog, the combo compatibility filter and the thinking-budget translator
+  // actually read. Assert the resolved view so a downstream default cannot quietly
+  // re-advertise a capability the executor does not have.
+  for (const model of gemini_webProvider.models) {
+    const input = { provider: "gemini-web", model: model.id };
+    assert.equal(supportsReasoning(input), false, `${model.id} resolved reasoning must be false`);
+    assert.equal(
+      supportsToolCalling(input),
+      false,
+      `${model.id} resolved NATIVE tool calling must be false — prompt emulation is advertised ` +
+        'separately as toolCalling:"emulated" on the provider constant'
+    );
+  }
+});
+
+test("#9356 the provider still advertises emulated tool calling, so #7286 combos keep routing", () => {
+  // Guard against over-correcting: dropping the emulation advertisement here would
+  // make filterTargetsByRequestCompatibility fail these targets closed and break
+  // emulation-only combos (#5240 / #8488).
+  assert.equal(providerSupportsEmulatedToolCalling("gemini-web"), true);
+  assert.equal(providerSupportsEmulatedToolCalling("gweb"), true);
+});