chore(main): release 0.31.4 (#611 )

🤖 I have created a release *beep* *boop* --- ## [0.31.4](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.31.3...v0.31.4) (2026-04-28) ### Bug Fixes * gate auto mode on model support ([#604](https://github.com/agentclientprotocol/claude-agent-acp/issues/604)) ([ec47d34](ec47d3446f)) --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). Co-authored-by: acp-release-bot[bot] <246668977+acp-release-bot[bot]@users.noreply.github.com>
fix: gate auto mode on model support (#604 )
2026-10-27 12:40:32 +00:00 · 2026-04-28 18:10:28 +02:00 · 2026-04-28 16:08:46 +00:00 · 2026-04-28 16:59:32 +02:00 · 2026-04-28 16:57:58 +02:00 · 2026-04-28 14:54:53 +00:00
9 changed files with 970 additions and 240 deletions
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "0.31.1"
+  ".": "0.31.4"
 }
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,26 @@
 # Changelog

+## [0.31.4](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.31.3...v0.31.4) (2026-04-28)
+
+
+### Bug Fixes
+
+* gate auto mode on model support ([#604](https://github.com/agentclientprotocol/claude-agent-acp/issues/604)) ([ec47d34](https://github.com/agentclientprotocol/claude-agent-acp/commit/ec47d3446fa22e5895621f57c0a4497dbe044505))
+
+## [0.31.3](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.31.2...v0.31.3) (2026-04-28)
+
+
+### Bug Fixes
+
+* Rename effort config category to thought_level ([#609](https://github.com/agentclientprotocol/claude-agent-acp/issues/609)) ([76b4e96](https://github.com/agentclientprotocol/claude-agent-acp/commit/76b4e9650832e59a6b4915ad898fc66a065022fa))
+
+## [0.31.2](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.31.1...v0.31.2) (2026-04-28)
+
+
+### Bug Fixes
+
+* tolerate invalid values in settings.json ([#601](https://github.com/agentclientprotocol/claude-agent-acp/issues/601)) ([67af018](https://github.com/agentclientprotocol/claude-agent-acp/commit/67af018d0216238d8f3cd5bad04a55200518239b))
+
 ## [0.31.1](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.31.0...v0.31.1) (2026-04-27)


--- a/package-lock.json
+++ b/package-lock.json
@@ -1,16 +1,16 @@
 {
  "name": "@agentclientprotocol/claude-agent-acp",
-  "version": "0.31.1",
+  "version": "0.31.4",
  "lockfileVersion": 3,
  "requires": true,
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      "license": "Apache-2.0",
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+      "integrity": "sha512-LwuHQI4pDOYVKvmH2dkaJo6YZCSgouVgnS/z7yBPKBMvgtBvyLqiLy9Z6b7+m/TRcX1NFYUqZetI5Y+aT4GEfg==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/types": "8.59.0",
-        "@typescript-eslint/visitor-keys": "8.59.0"
+        "@typescript-eslint/types": "8.59.1",
+        "@typescript-eslint/visitor-keys": "8.59.1"
      },
      "engines": {
        "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -1041,9 +1011,9 @@
      }
    },
    "node_modules/@typescript-eslint/tsconfig-utils": {
-      "version": "8.59.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/tsconfig-utils/-/tsconfig-utils-8.59.0.tgz",
-      "integrity": "sha512-91Sbl3s4Kb3SybliIY6muFBmHVv+pYXfybC4Oolp3dvk8BvIE3wOPc+403CWIT7mJNkfQRGtdqghzs2+Z91Tqg==",
+      "version": "8.59.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/tsconfig-utils/-/tsconfig-utils-8.59.1.tgz",
+      "integrity": "sha512-/0nEyPbX7gRsk0Uwfe4ALwwgxuA66d/l2mhRDNlAvaj4U3juhUtJNq0DsY8M2AYwwb9rEq2hrC3IcIcEt++iJA==",
      "dev": true,
      "license": "MIT",
      "engines": {
@@ -1058,15 +1028,15 @@
      }
    },
    "node_modules/@typescript-eslint/type-utils": {
-      "version": "8.59.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-8.59.0.tgz",
-      "integrity": "sha512-3TRiZaQSltGqGeNrJzzr1+8YcEobKH9rHnqIp/1psfKFmhRQDNMGP5hBufanYTGznwShzVLs3Mz+gDN7HkWfXg==",
+      "version": "8.59.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-8.59.1.tgz",
+      "integrity": "sha512-klWPBR2ciQHS3f++ug/mVnWKPjBUo7icEL3FAO1lhAR1Z1i5NQYZ1EannMSRYcq5qCv5wNALlXr6fksRHyYl7w==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/types": "8.59.0",
-        "@typescript-eslint/typescript-estree": "8.59.0",
-        "@typescript-eslint/utils": "8.59.0",
+        "@typescript-eslint/types": "8.59.1",
+        "@typescript-eslint/typescript-estree": "8.59.1",
+        "@typescript-eslint/utils": "8.59.1",
        "debug": "^4.4.3",
        "ts-api-utils": "^2.5.0"
      },
@@ -1083,9 +1053,9 @@
      }
    },
    "node_modules/@typescript-eslint/types": {
-      "version": "8.59.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-8.59.0.tgz",
-      "integrity": "sha512-nLzdsT1gdOgFxxxwrlNVUBzSNBEEHJ86bblmk4QAS6stfig7rcJzWKqCyxFy3YRRHXDWEkb2NralA1nOYkkm/A==",
+      "version": "8.59.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-8.59.1.tgz",
+      "integrity": "sha512-ZDCjgccSdYPw5Bxh+my4Z0lJU96ZDN7jbBzvmEn0FZx3RtU1C7VWl6NbDx94bwY3V5YsgwRzJPOgeY2Q/nLG8A==",
      "dev": true,
      "license": "MIT",
      "engines": {
@@ -1097,16 +1067,16 @@
      }
    },
    "node_modules/@typescript-eslint/typescript-estree": {
-      "version": "8.59.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-8.59.0.tgz",
-      "integrity": "sha512-O9Re9P1BmBLFJyikRbQpLku/QA3/AueZNO9WePLBwQrvkixTmDe8u76B6CYUAITRl/rHawggEqUGn5QIkVRLMw==",
+      "version": "8.59.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-8.59.1.tgz",
+      "integrity": "sha512-OUd+vJS05sSkOip+BkZ/2NS8RMxrAAJemsC6vU3kmfLyeaJT0TftHkV9mcx2107MmsBVXXexhVu4F0TZXyMl4g==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/project-service": "8.59.0",
-        "@typescript-eslint/tsconfig-utils": "8.59.0",
-        "@typescript-eslint/types": "8.59.0",
-        "@typescript-eslint/visitor-keys": "8.59.0",
+        "@typescript-eslint/project-service": "8.59.1",
+        "@typescript-eslint/tsconfig-utils": "8.59.1",
+        "@typescript-eslint/types": "8.59.1",
+        "@typescript-eslint/visitor-keys": "8.59.1",
        "debug": "^4.4.3",
        "minimatch": "^10.2.2",
        "semver": "^7.7.3",
@@ -1125,16 +1095,16 @@
      }
    },
    "node_modules/@typescript-eslint/utils": {
-      "version": "8.59.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-8.59.0.tgz",
-      "integrity": "sha512-I1R/K7V07XsMJ12Oaxg/O9GfrysGTmCRhvZJBv0RE0NcULMzjqVpR5kRRQjHsz3J/bElU7HwCO7zkqL+MSUz+g==",
+      "version": "8.59.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-8.59.1.tgz",
+      "integrity": "sha512-3pIeoXhCeYH9FSCBI8P3iNwJlGuzPlYKkTlen2O9T1DSeeg8UG8jstq6BLk+Mda0qup7mgk4z4XL4OzRaxZ8LA==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
        "@eslint-community/eslint-utils": "^4.9.1",
-        "@typescript-eslint/scope-manager": "8.59.0",
-        "@typescript-eslint/types": "8.59.0",
-        "@typescript-eslint/typescript-estree": "8.59.0"
+        "@typescript-eslint/scope-manager": "8.59.1",
+        "@typescript-eslint/types": "8.59.1",
+        "@typescript-eslint/typescript-estree": "8.59.1"
      },
      "engines": {
        "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -1149,13 +1119,13 @@
      }
    },
    "node_modules/@typescript-eslint/visitor-keys": {
-      "version": "8.59.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-8.59.0.tgz",
-      "integrity": "sha512-/uejZt4dSere1bx12WLlPfv8GktzcaDtuJ7s42/HEZ5zGj9oxRaD4bj7qwSunXkf+pbAhFt2zjpHYUiT5lHf0Q==",
+      "version": "8.59.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-8.59.1.tgz",
+      "integrity": "sha512-LdDNl6C5iJExcM0Yh0PwAIBb9PrSiCsWamF/JyEZawm3kFDnRoaq3LGE4bpyRao/fWeGKKyw7icx0YxrLFC5Cg==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/types": "8.59.0",
+        "@typescript-eslint/types": "8.59.1",
        "eslint-visitor-keys": "^5.0.0"
      },
      "engines": {
@@ -1672,9 +1642,9 @@
      }
    },
    "node_modules/es-module-lexer": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/es-module-lexer/-/es-module-lexer-2.0.0.tgz",
-      "integrity": "sha512-5POEcUuZybH7IdmGsD8wlf0AI55wMecM9rVBTI/qEAy2c1kTOm3DjFYjrBdI2K3BaJjJYfYFeRtM0t9ssnRuxw==",
+      "version": "2.1.0",
+      "resolved": "https://registry.npmjs.org/es-module-lexer/-/es-module-lexer-2.1.0.tgz",
+      "integrity": "sha512-n27zTYMjYu1aj4MjCWzSP7G9r75utsaoc8m61weK+W8JMBGGQybd43GstCXZ3WNmSFtGT9wi59qQTW6mhTR5LQ==",
      "dev": true,
      "license": "MIT"
    },
@@ -2031,9 +2001,9 @@
      }
    },
    "node_modules/express-rate-limit": {
-      "version": "8.4.0",
-      "resolved": "https://registry.npmjs.org/express-rate-limit/-/express-rate-limit-8.4.0.tgz",
-      "integrity": "sha512-gDK8yiqKxrGta+3WtON59arrrw6GLmadA1qoFgYXzdcch8fmKDID2XqO8itsi3f1wufXYPT51387dN6cvVBS3Q==",
+      "version": "8.4.1",
+      "resolved": "https://registry.npmjs.org/express-rate-limit/-/express-rate-limit-8.4.1.tgz",
+      "integrity": "sha512-NGVYwQSAyEQgzxX1iCM978PP9AdO/hW93gMcF6ZwQCm+rFvLsBH6w4xcXWTcliS8La5EPRN3p9wzItqBwJrfNw==",
      "license": "MIT",
      "dependencies": {
        "ip-address": "10.1.0"
@@ -2440,9 +2410,9 @@
      "license": "ISC"
    },
    "node_modules/jose": {
-      "version": "6.2.2",
-      "resolved": "https://registry.npmjs.org/jose/-/jose-6.2.2.tgz",
-      "integrity": "sha512-d7kPDd34KO/YnzaDOlikGpOurfF0ByC2sEV4cANCtdqLlTfBlw2p14O/5d/zv40gJPbIQxfES3nSx1/oYNyuZQ==",
+      "version": "6.2.3",
+      "resolved": "https://registry.npmjs.org/jose/-/jose-6.2.3.tgz",
+      "integrity": "sha512-YYVDInQKFJfR/xa3ojUTl8c2KoTwiL1R5Wg9YCydwH0x0B9grbzlg5HC7mMjCtUJjbQ/YnGEZIhI5tCgfTb4Hw==",
      "license": "MIT",
      "funding": {
        "url": "https://github.com/sponsors/panva"
@@ -2654,9 +2624,6 @@
        "arm64"
      ],
      "dev": true,
-      "libc": [
-        "glibc"
-      ],
      "license": "MPL-2.0",
      "optional": true,
      "os": [
@@ -2678,9 +2645,6 @@
        "arm64"
      ],
      "dev": true,
-      "libc": [
-        "musl"
-      ],
      "license": "MPL-2.0",
      "optional": true,
      "os": [
@@ -2702,9 +2666,6 @@
        "x64"
      ],
      "dev": true,
-      "libc": [
-        "glibc"
-      ],
      "license": "MPL-2.0",
      "optional": true,
      "os": [
@@ -2726,9 +2687,6 @@
        "x64"
      ],
      "dev": true,
-      "libc": [
-        "musl"
-      ],
      "license": "MPL-2.0",
      "optional": true,
      "os": [
@@ -3107,9 +3065,9 @@
      }
    },
    "node_modules/postcss": {
-      "version": "8.5.10",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.10.tgz",
-      "integrity": "sha512-pMMHxBOZKFU6HgAZ4eyGnwXF/EvPGGqUr0MnZ5+99485wwW41kW91A4LOGxSHhgugZmSChL5AlElNdwlNgcnLQ==",
+      "version": "8.5.12",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.12.tgz",
+      "integrity": "sha512-W62t/Se6rA0Az3DfCL0AqJwXuKwBeYg6nOaIgzP+xZ7N5BFCI7DYi1qs6ygUYT6rvfi6t9k65UMLJC+PHZpDAA==",
      "dev": true,
      "funding": [
        {
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
  "publishConfig": {
    "access": "public"
  },
-  "version": "0.31.1",
+  "version": "0.31.4",
  "description": "An ACP-compatible coding agent powered by the Claude Agent SDK (TypeScript)",
  "main": "dist/lib.js",
  "types": "dist/lib.d.ts",
@@ -60,16 +60,16 @@
  "author": "Zed Industries",
  "license": "Apache-2.0",
  "dependencies": {
-    "@agentclientprotocol/sdk": "0.20.0",
-    "@anthropic-ai/claude-agent-sdk": "0.2.119",
+    "@agentclientprotocol/sdk": "0.21.0",
+    "@anthropic-ai/claude-agent-sdk": "0.2.121",
    "zod": "^3.25.0 || ^4.0.0"
  },
  "devDependencies": {
    "@anthropic-ai/sdk": "0.89.0",
    "@eslint/js": "10.0.1",
    "@types/node": "25.6.0",
-    "@typescript-eslint/eslint-plugin": "8.59.0",
-    "@typescript-eslint/parser": "8.59.0",
+    "@typescript-eslint/eslint-plugin": "8.59.1",
+    "@typescript-eslint/parser": "8.59.1",
    "eslint": "10.2.1",
    "eslint-config-prettier": "10.1.8",
    "globals": "17.5.0",
--- a/src/acp-agent.ts
+++ b/src/acp-agent.ts
@@ -385,29 +385,36 @@ const PERMISSION_MODE_ALIASES: Record<string, PermissionMode> = {
  bypass: "bypassPermissions",
 };

-export function resolvePermissionMode(defaultMode?: unknown): PermissionMode {
+export function resolvePermissionMode(
+  defaultMode?: unknown,
+  logger: Logger = console,
+): PermissionMode {
  if (defaultMode === undefined) {
    return "default";
  }

  if (typeof defaultMode !== "string") {
-    throw new Error("Invalid permissions.defaultMode: expected a string.");
+    logger.error("Ignoring permissions.defaultMode from settings: expected a string.");
+    return "default";
  }

  const normalized = defaultMode.trim().toLowerCase();
  if (normalized === "") {
-    throw new Error("Invalid permissions.defaultMode: expected a non-empty string.");
+    logger.error("Ignoring permissions.defaultMode from settings: expected a non-empty string.");
+    return "default";
  }

  const mapped = PERMISSION_MODE_ALIASES[normalized];
  if (!mapped) {
-    throw new Error(`Invalid permissions.defaultMode: ${defaultMode}.`);
+    logger.error(`Ignoring permissions.defaultMode from settings: unknown value '${defaultMode}'.`);
+    return "default";
  }

  if (mapped === "bypassPermissions" && !ALLOW_BYPASS) {
-    throw new Error(
-      "Invalid permissions.defaultMode: bypassPermissions is not available when running as root.",
+    logger.error(
+      "Ignoring permissions.defaultMode from settings: bypassPermissions is not available when running as root.",
    );
+    return "default";
  }

  return mapped;
@@ -1302,7 +1309,7 @@ export class ClaudeAcpAgent implements Agent {
    // effort changes and effort changes induced by a model switch go through
    // the same path.

-    await this.applyConfigOptionValue(session, params.configId, resolvedValue);
+    await this.applyConfigOptionValue(params.sessionId, session, params.configId, resolvedValue);

    return { configOptions: session.configOptions };
  }
@@ -1319,8 +1326,17 @@ export class ClaudeAcpAgent implements Agent {
      default:
        throw new Error("Invalid Mode");
    }
+
+    const session = this.sessions[sessionId];
+    if (!session) {
+      throw new Error("Session not found");
+    }
+    if (!session.modes.availableModes.some((mode) => mode.id === modeId)) {
+      throw new Error(`Mode ${modeId} is not available in this session`);
+    }
+
    try {
-      await this.sessions[sessionId].query.setPermissionMode(modeId);
+      await session.query.setPermissionMode(modeId);
    } catch (error) {
      if (error instanceof Error) {
        if (!error.message) {
@@ -1390,7 +1406,7 @@ export class ClaudeAcpAgent implements Agent {
      }

      if (toolName === "ExitPlanMode") {
-        const options = [
+        const optionsAll = [
          { kind: "allow_always", name: 'Yes, and use "auto" mode', optionId: "auto" },
          {
            kind: "allow_always",
@@ -1401,12 +1417,20 @@ export class ClaudeAcpAgent implements Agent {
          { kind: "reject_once", name: "No, keep planning", optionId: "plan" },
        ];
        if (ALLOW_BYPASS) {
-          options.unshift({
+          optionsAll.unshift({
            kind: "allow_always",
            name: "Yes, and bypass permissions",
            optionId: "bypassPermissions",
          });
        }
+        // Filter against the session's currently-advertised modes so we never
+        // present options the active model can't honor (e.g. `auto` on Haiku).
+        // `bypassPermissions` is already covered by `availableModes` via
+        // `buildAvailableModes`/`ALLOW_BYPASS`. The `plan` option is a
+        // "keep planning" reject path; it's always present in `availableModes`.
+        const options = optionsAll.filter((o) =>
+          session.modes.availableModes.some((m) => m.id === o.optionId),
+        );

        const response = await this.client.requestPermission({
          options,
@@ -1425,27 +1449,30 @@ export class ClaudeAcpAgent implements Agent {
        if (signal.aborted || response.outcome?.outcome === "cancelled") {
          throw new Error("Tool use aborted");
        }
+        const selectedMode =
+          response.outcome?.outcome === "selected" ? response.outcome.optionId : undefined;
+        const selectedModeWasOffered = options.some((option) => option.optionId === selectedMode);
        if (
-          response.outcome?.outcome === "selected" &&
-          (response.outcome.optionId === "default" ||
-            response.outcome.optionId === "acceptEdits" ||
-            response.outcome.optionId === "auto" ||
-            response.outcome.optionId === "bypassPermissions")
+          selectedModeWasOffered &&
+          (selectedMode === "default" ||
+            selectedMode === "acceptEdits" ||
+            selectedMode === "auto" ||
+            selectedMode === "bypassPermissions")
        ) {
          await this.client.sessionUpdate({
            sessionId,
            update: {
              sessionUpdate: "current_mode_update",
-              currentModeId: response.outcome.optionId,
+              currentModeId: selectedMode,
            },
          });
-          await this.updateConfigOption(sessionId, "mode", response.outcome.optionId);
+          await this.updateConfigOption(sessionId, "mode", selectedMode);

          return {
            behavior: "allow",
            updatedInput: toolInput,
            updatedPermissions: suggestions ?? [
-              { type: "setMode", mode: response.outcome.optionId, destination: "session" },
+              { type: "setMode", mode: selectedMode, destination: "session" },
            ],
          };
        } else {
@@ -1543,7 +1570,7 @@ export class ClaudeAcpAgent implements Agent {
    const session = this.sessions[sessionId];
    if (!session) return;

-    await this.applyConfigOptionValue(session, configId, value);
+    await this.applyConfigOptionValue(sessionId, session, configId, value);

    await this.client.sessionUpdate({
      sessionId,
@@ -1555,13 +1582,16 @@ export class ClaudeAcpAgent implements Agent {
  }

  private async applyConfigOptionValue(
+    sessionId: string,
    session: Session,
    configId: string,
    value: string,
  ): Promise<void> {
-    // Sync top-level session state
    if (configId === "mode") {
      session.modes = { ...session.modes, currentModeId: value };
+      session.configOptions = session.configOptions.map((o) =>
+        o.id === configId && typeof o.currentValue === "string" ? { ...o, currentValue: value } : o,
+      );
    } else if (configId === "model") {
      if (session.models.currentModelId !== value) {
        // The cached context window was learned for the previous model; reset
@@ -1571,10 +1601,38 @@ export class ClaudeAcpAgent implements Agent {
        session.contextWindowSize = inferContextWindowFromModel(value) ?? DEFAULT_CONTEXT_WINDOW;
      }
      session.models = { ...session.models, currentModelId: value };
-    }

-    // Update configOptions
-    if (configId === "model") {
+      // Recompute availableModes for the new model and clamp the current
+      // mode if the SDK no longer offers it (today: "auto" on Haiku).
+      // `ModelInfo.supportsAutoMode` is the canonical SDK signal.
+      const newModelInfo = session.modelInfos.find((m) => m.value === value);
+      const newAvailableModes = buildAvailableModes(newModelInfo);
+      // Capture BEFORE mutating session.modes so the log message reflects
+      // the invalidated mode rather than "default".
+      const previousModeId = session.modes.currentModeId;
+      let modeDowngraded = false;
+      if (!newAvailableModes.some((m) => m.id === previousModeId)) {
+        session.modes = {
+          availableModes: newAvailableModes,
+          currentModeId: "default",
+        };
+        try {
+          await session.query.setPermissionMode("default");
+        } catch (err) {
+          // Failing the entire model switch over a bookkeeping sync error is
+          // worse UX than logging and continuing; the user explicitly asked
+          // to change models. The next setPermissionMode from the user will
+          // either succeed or surface a fresh error.
+          this.logger.error(
+            `Failed to sync permissionMode to "default" after model switch invalidated "${previousModeId}":`,
+            err,
+          );
+        }
+        modeDowngraded = true;
+      } else {
+        session.modes = { ...session.modes, availableModes: newAvailableModes };
+      }
+
      // Rebuild config options since effort levels depend on the selected model
      const effortOpt = session.configOptions.find((o) => o.id === "effort");
      const currentEffort =
@@ -1595,6 +1653,22 @@ export class ClaudeAcpAgent implements Agent {
          effortLevel: newEffort as Settings["effortLevel"],
        });
      }
+
+      // Emit current_mode_update only after session.modes AND
+      // session.configOptions have been fully reconciled. This way, a failure
+      // in the configOptions/effort rebuild above can't leave the client with
+      // a clamped currentModeId but stale configOptions, and the notification
+      // still precedes the caller's config_option_update so order-sensitive
+      // clients update currentModeId before re-rendering the option list.
+      if (modeDowngraded) {
+        await this.client.sessionUpdate({
+          sessionId,
+          update: {
+            sessionUpdate: "current_mode_update",
+            currentModeId: "default",
+          },
+        });
+      }
    } else {
      session.configOptions = session.configOptions.map((o) =>
        o.id === configId && typeof o.currentValue === "string" ? { ...o, currentValue: value } : o,
@@ -1720,6 +1794,7 @@ export class ClaudeAcpAgent implements Agent {

    const permissionMode = resolvePermissionMode(
      settingsManager.getSettings().permissions?.defaultMode,
+      this.logger,
    );

    // Extract options from _meta if provided
@@ -1858,46 +1933,52 @@ export class ClaudeAcpAgent implements Agent {
      );
    }

-    const models = await getAvailableModels(q, initializationResult.models, settingsManager);
+    const models = await getAvailableModels(
+      q,
+      initializationResult.models,
+      settingsManager,
+      this.logger,
+    );

-    const availableModes = [
-      {
-        id: "auto",
-        name: "Auto",
-        description: "Use a model classifier to approve/deny permission prompts",
-      },
-      {
-        id: "default",
-        name: "Default",
-        description: "Standard behavior, prompts for dangerous operations",
-      },
-      {
-        id: "acceptEdits",
-        name: "Accept Edits",
-        description: "Auto-accept file edit operations",
-      },
-      {
-        id: "plan",
-        name: "Plan Mode",
-        description: "Planning mode, no actual tool execution",
-      },
-      {
-        id: "dontAsk",
-        name: "Don't Ask",
-        description: "Don't prompt for permissions, deny if not pre-approved",
-      },
-    ];
-    // Only works in non-root mode
-    if (ALLOW_BYPASS) {
-      availableModes.push({
-        id: "bypassPermissions",
-        name: "Bypass Permissions",
-        description: "Bypass all permission checks",
-      });
+    // Gate `auto` (and future model-specific modes) on the resolved model's
+    // `ModelInfo`. See `buildAvailableModes` for the canonical SDK signal.
+    const currentModelInfo = initializationResult.models.find(
+      (m) => m.value === models.currentModelId,
+    );
+    const availableModes = buildAvailableModes(currentModelInfo);
+
+    // Clamp `permissionMode` if the resolved session does not offer it. The
+    // common case is `permissions.defaultMode: "auto"` resolving to a model
+    // that does not support auto mode (e.g. Haiku); without this clamp the
+    // SDK would later throw `"auto mode unavailable for this model"` from
+    // `setPermissionMode`. Keep `permissionMode` as the resolved user intent
+    // (matches what was passed into `options.permissionMode` above) and use
+    // `effectiveMode` for the post-clamp value the session actually runs in.
+    let effectiveMode: PermissionMode = permissionMode;
+    if (!availableModes.some((m) => m.id === effectiveMode)) {
+      if (effectiveMode === "auto") {
+        this.logger.error(
+          `permissions.defaultMode "auto" is not available for model ` +
+            `"${models.currentModelId}"; falling back to "default".`,
+        );
+      } else {
+        this.logger.error(
+          `permissions.defaultMode "${effectiveMode}" is not available in ` +
+            `this session; falling back to "default".`,
+        );
+      }
+      effectiveMode = "default";
+      // Sync the SDK so it doesn't keep "auto" cached internally. Wrapped in
+      // try/catch since failing here would abort session creation entirely.
+      try {
+        await q.setPermissionMode("default");
+      } catch (err) {
+        this.logger.error("Failed to sync clamped permissionMode to SDK:", err);
+      }
    }

    const modes = {
-      currentModeId: permissionMode,
+      currentModeId: effectiveMode,
      availableModes,
    };

@@ -2040,6 +2121,58 @@ function createEnvForGateway(gatewayMeta?: GatewayAuthMeta) {
  };
 }

+/**
+ * Build the list of permission modes the agent will advertise for the given
+ * model. `auto` is gated by `ModelInfo.supportsAutoMode === true`, which is
+ * the SDK's model-level availability signal. `undefined`/`false` both exclude
+ * `auto`. `bypassPermissions` is still gated by `ALLOW_BYPASS`.
+ */
+function buildAvailableModes(modelInfo: ModelInfo | undefined): SessionModeState["availableModes"] {
+  const modes: SessionModeState["availableModes"] = [];
+
+  // Only advertise "auto" when the SDK reports the model supports it.
+  if (modelInfo?.supportsAutoMode === true) {
+    modes.push({
+      id: "auto",
+      name: "Auto",
+      description: "Use a model classifier to approve/deny permission prompts",
+    });
+  }
+
+  modes.push(
+    {
+      id: "default",
+      name: "Default",
+      description: "Standard behavior, prompts for dangerous operations",
+    },
+    {
+      id: "acceptEdits",
+      name: "Accept Edits",
+      description: "Auto-accept file edit operations",
+    },
+    {
+      id: "plan",
+      name: "Plan Mode",
+      description: "Planning mode, no actual tool execution",
+    },
+    {
+      id: "dontAsk",
+      name: "Don't Ask",
+      description: "Don't prompt for permissions, deny if not pre-approved",
+    },
+  );
+
+  if (ALLOW_BYPASS) {
+    modes.push({
+      id: "bypassPermissions",
+      name: "Bypass Permissions",
+      description: "Bypass all permission checks",
+    });
+  }
+
+  return modes;
+}
+
 function buildConfigOptions(
  modes: SessionModeState,
  models: SessionModelState,
@@ -2106,7 +2239,7 @@ function buildConfigOptions(
      id: "effort",
      name: "Effort",
      description: "Available effort levels for this model",
-      category: "effort",
+      category: "thought_level",
      type: "select",
      currentValue: validEffort,
      options: effortOptions,
@@ -2189,10 +2322,27 @@ function resolveModelPreference(models: ModelInfo[], preference: string): ModelI
  return bestMatch;
 }

+function resolveSettingsModel(
+  models: ModelInfo[],
+  settingsModel: unknown,
+  logger: Logger,
+): ModelInfo | null {
+  if (settingsModel === undefined) {
+    return null;
+  }
+  if (typeof settingsModel !== "string") {
+    const typeLabel = settingsModel === null ? "null" : typeof settingsModel;
+    logger.error(`Ignoring model from settings: expected a string, got ${typeLabel}.`);
+    return null;
+  }
+  return resolveModelPreference(models, settingsModel);
+}
+
 async function getAvailableModels(
  query: Query,
  models: ModelInfo[],
  settingsManager: SettingsManager,
+  logger: Logger,
 ): Promise<SessionModelState> {
  const settings = settingsManager.getSettings();

@@ -2207,8 +2357,8 @@ async function getAvailableModels(
    if (match) {
      currentModel = match;
    }
-  } else if (settings.model) {
-    const match = resolveModelPreference(models, settings.model);
+  } else {
+    const match = resolveSettingsModel(models, settings.model, logger);
    if (match) {
      currentModel = match;
    }
--- a/src/tests/acp-agent-settings.test.ts
+++ b/src/tests/acp-agent-settings.test.ts
@@ -145,12 +145,12 @@ describe("ClaudeAcpAgent settings", () => {
    expect(response.modes.currentModeId).toBe("default");
  });

-  it("throws when permissions.defaultMode is not a string", async () => {
+  it("falls back to 'default' when permissions.defaultMode is invalid", async () => {
    await fs.promises.writeFile(
      path.join(tempDir, "settings.json"),
      JSON.stringify({
        permissions: {
-          defaultMode: 123,
+          defaultMode: "not-a-real-mode",
        },
      }),
    );
@@ -158,18 +158,208 @@ describe("ClaudeAcpAgent settings", () => {
    const projectDir = path.join(tempDir, "project");
    await fs.promises.mkdir(projectDir, { recursive: true });

-    mockQuery();
+    const { getCapturedOptions } = mockQuery();

    const { ClaudeAcpAgent } = await import("../acp-agent.js");
    const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());

-    await expect(
-      (agent as any).createSession({
+    const response = await (agent as any).createSession({
+      cwd: projectDir,
+      mcpServers: [],
+      _meta: { disableBuiltInTools: true },
+    });
+
+    // Bad mode is ignored at the usage site; session creation must not throw.
+    expect(getCapturedOptions().permissionMode).toBe("default");
+    expect(response.modes.currentModeId).toBe("default");
+  });
+
+  it("ignores model from settings when it is not a string", async () => {
+    await fs.promises.writeFile(
+      path.join(tempDir, "settings.json"),
+      JSON.stringify({
+        model: 123,
+      }),
+    );
+
+    const projectDir = path.join(tempDir, "project");
+    await fs.promises.mkdir(projectDir, { recursive: true });
+
+    const { setModelSpy } = mockQuery();
+
+    const { ClaudeAcpAgent } = await import("../acp-agent.js");
+    const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+    const response = await (agent as any).createSession({
+      cwd: projectDir,
+      mcpServers: [],
+      _meta: { disableBuiltInTools: true },
+    });
+
+    // Bad model is ignored at the usage site; falls back to the first SDK model.
+    expect(setModelSpy).toHaveBeenCalledWith("claude-sonnet-4-5");
+    expect(response.models.currentModelId).toBe("claude-sonnet-4-5");
+  });
+
+  describe("auto mode availability per model", () => {
+    function mockQueryWithModels(models: any[]): {
+      getCapturedOptions: () => any;
+      setModelSpy: ReturnType<typeof vi.fn>;
+      setPermissionModeSpy: ReturnType<typeof vi.fn>;
+    } {
+      let capturedOptions: any;
+      const setModelSpy = vi.fn();
+      const setPermissionModeSpy = vi.fn();
+      querySpy.mockImplementation(({ options }: any) => {
+        capturedOptions = options;
+        return {
+          initializationResult: async () => ({ models }),
+          setModel: setModelSpy,
+          setPermissionMode: setPermissionModeSpy,
+          supportedCommands: async () => [],
+        } as any;
+      });
+      return {
+        getCapturedOptions: () => capturedOptions,
+        setModelSpy,
+        setPermissionModeSpy,
+      };
+    }
+
+    it("omits `auto` from availableModes when the resolved model lacks supportsAutoMode", async () => {
+      const projectDir = path.join(tempDir, "project");
+      await fs.promises.mkdir(projectDir, { recursive: true });
+
+      mockQueryWithModels([
+        {
+          value: "claude-haiku-4-5",
+          displayName: "Claude Haiku",
+          description: "Fast",
+          // supportsAutoMode intentionally omitted
+        },
+      ]);
+
+      const { ClaudeAcpAgent } = await import("../acp-agent.js");
+      const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+      const response = await (agent as any).createSession({
        cwd: projectDir,
        mcpServers: [],
        _meta: { disableBuiltInTools: true },
-      }),
-    ).rejects.toThrow("Invalid permissions.defaultMode");
+      });
+
+      const modeIds: string[] = response.modes.availableModes.map((m: any) => m.id);
+      expect(modeIds).not.toContain("auto");
+      expect(modeIds).toEqual(
+        expect.arrayContaining(["default", "acceptEdits", "plan", "dontAsk"]),
+      );
+    });
+
+    it("includes `auto` when the resolved model has supportsAutoMode: true", async () => {
+      const projectDir = path.join(tempDir, "project");
+      await fs.promises.mkdir(projectDir, { recursive: true });
+
+      mockQueryWithModels([
+        {
+          value: "claude-opus-4-5",
+          displayName: "Claude Opus",
+          description: "Most capable",
+          supportsAutoMode: true,
+        },
+      ]);
+
+      const { ClaudeAcpAgent } = await import("../acp-agent.js");
+      const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+      const response = await (agent as any).createSession({
+        cwd: projectDir,
+        mcpServers: [],
+        _meta: { disableBuiltInTools: true },
+      });
+
+      const modeIds: string[] = response.modes.availableModes.map((m: any) => m.id);
+      expect(modeIds).toContain("auto");
+    });
+
+    it("clamps permissions.defaultMode='auto' to 'default' on a model that lacks supportsAutoMode", async () => {
+      await fs.promises.writeFile(
+        path.join(tempDir, "settings.json"),
+        JSON.stringify({ permissions: { defaultMode: "auto" } }),
+      );
+
+      const projectDir = path.join(tempDir, "project");
+      await fs.promises.mkdir(projectDir, { recursive: true });
+
+      const { getCapturedOptions, setPermissionModeSpy } = mockQueryWithModels([
+        {
+          value: "claude-haiku-4-5",
+          displayName: "Claude Haiku",
+          description: "Fast",
+          // supportsAutoMode intentionally omitted
+        },
+      ]);
+
+      const errorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+      try {
+        const { ClaudeAcpAgent } = await import("../acp-agent.js");
+        const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+        const response = await (agent as any).createSession({
+          cwd: projectDir,
+          mcpServers: [],
+          _meta: { disableBuiltInTools: true },
+        });
+
+        // Options.permissionMode is built before init resolves, so it still
+        // carries the user-typed value; the SDK was synced via
+        // setPermissionMode after we discovered the model can't honor it.
+        expect(getCapturedOptions().permissionMode).toBe("auto");
+        expect(setPermissionModeSpy).toHaveBeenCalledWith("default");
+        expect(response.modes.currentModeId).toBe("default");
+        expect(response.modes.availableModes.map((m: any) => m.id)).not.toContain("auto");
+
+        // A descriptive warning was logged so operators see the clamp.
+        const messages = errorSpy.mock.calls.map((c) => c.join(" "));
+        expect(messages.some((m) => m.includes("auto") && m.includes("claude-haiku-4-5"))).toBe(
+          true,
+        );
+      } finally {
+        errorSpy.mockRestore();
+      }
+    });
+
+    it("does not clamp permissions.defaultMode='auto' on a model that supports auto", async () => {
+      await fs.promises.writeFile(
+        path.join(tempDir, "settings.json"),
+        JSON.stringify({ permissions: { defaultMode: "auto" } }),
+      );
+
+      const projectDir = path.join(tempDir, "project");
+      await fs.promises.mkdir(projectDir, { recursive: true });
+
+      const { getCapturedOptions, setPermissionModeSpy } = mockQueryWithModels([
+        {
+          value: "claude-opus-4-5",
+          displayName: "Claude Opus",
+          description: "Most capable",
+          supportsAutoMode: true,
+        },
+      ]);
+
+      const { ClaudeAcpAgent } = await import("../acp-agent.js");
+      const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+      const response = await (agent as any).createSession({
+        cwd: projectDir,
+        mcpServers: [],
+        _meta: { disableBuiltInTools: true },
+      });
+
+      expect(getCapturedOptions().permissionMode).toBe("auto");
+      expect(setPermissionModeSpy).not.toHaveBeenCalled();
+      expect(response.modes.currentModeId).toBe("auto");
+    });
  });

  it("resolves model aliases like opus[1m] to the correct model", async () => {
--- a/src/tests/acp-agent.test.ts
+++ b/src/tests/acp-agent.test.ts
@@ -2502,7 +2502,12 @@ describe("usage_update computation", () => {
    const session = agent.sessions["test-session"];
    expect(session.contextWindowSize).toBe(200000);

-    await (agent as any).applyConfigOptionValue(session, "model", "claude-opus-4-6-1m");
+    await (agent as any).applyConfigOptionValue(
+      "test-session",
+      session,
+      "model",
+      "claude-opus-4-6-1m",
+    );
    expect(session.contextWindowSize).toBe(1000000);

    await agent.prompt({ sessionId: "test-session", prompt: [{ type: "text", text: "test" }] });
@@ -2587,7 +2592,12 @@ describe("usage_update computation", () => {
    session.models = { ...session.models, currentModelId: "claude-opus-4-6-1m" };

    // User flips the selector to a 200k model.
-    await (agent as any).applyConfigOptionValue(session, "model", "claude-sonnet-4-6");
+    await (agent as any).applyConfigOptionValue(
+      "test-session",
+      session,
+      "model",
+      "claude-sonnet-4-6",
+    );

    await agent.prompt({ sessionId: "test-session", prompt: [{ type: "text", text: "test" }] });

--- a/src/tests/resolve-permission-mode.test.ts
+++ b/src/tests/resolve-permission-mode.test.ts
@@ -1,5 +1,12 @@
-import { describe, it, expect } from "vitest";
-import { resolvePermissionMode } from "../acp-agent.js";
+import { describe, it, expect, vi } from "vitest";
+import { resolvePermissionMode, type Logger } from "../acp-agent.js";
+
+function mockLogger() {
+  const error = vi.fn<(...args: any[]) => void>();
+  const log = vi.fn<(...args: any[]) => void>();
+  const logger: Logger = { log, error };
+  return { logger, error, log };
+}

 describe("resolvePermissionMode", () => {
  it("returns 'default' when no mode is provided", () => {
@@ -26,18 +33,25 @@ describe("resolvePermissionMode", () => {
    expect(resolvePermissionMode("  dontAsk  ")).toBe("dontAsk");
  });

-  it("throws on non-string values", () => {
-    expect(() => resolvePermissionMode(123)).toThrow("expected a string");
-    expect(() => resolvePermissionMode(true)).toThrow("expected a string");
-    expect(() => resolvePermissionMode({})).toThrow("expected a string");
+  it("falls back to 'default' and logs on non-string values", () => {
+    for (const value of [123, true, {}]) {
+      const { logger, error } = mockLogger();
+      expect(resolvePermissionMode(value, logger)).toBe("default");
+      expect(error).toHaveBeenCalledWith(expect.stringContaining("expected a string"));
+    }
  });

-  it("throws on empty string", () => {
-    expect(() => resolvePermissionMode("")).toThrow("expected a non-empty string");
-    expect(() => resolvePermissionMode("  ")).toThrow("expected a non-empty string");
+  it("falls back to 'default' and logs on empty string", () => {
+    for (const value of ["", "  "]) {
+      const { logger, error } = mockLogger();
+      expect(resolvePermissionMode(value, logger)).toBe("default");
+      expect(error).toHaveBeenCalledWith(expect.stringContaining("expected a non-empty string"));
+    }
  });

-  it("throws on unknown mode", () => {
-    expect(() => resolvePermissionMode("yolo")).toThrow("Invalid permissions.defaultMode: yolo");
+  it("falls back to 'default' and logs on unknown mode", () => {
+    const { logger, error } = mockLogger();
+    expect(resolvePermissionMode("yolo", logger)).toBe("default");
+    expect(error).toHaveBeenCalledWith(expect.stringContaining("yolo"));
  });
 });
--- a/src/tests/session-config-options.test.ts
+++ b/src/tests/session-config-options.test.ts
@@ -811,4 +811,391 @@ describe("session config options", () => {
      );
    });
  });
+
+  describe("auto mode availability per model", () => {
+    /**
+     * Augment the session populated by `populateSession()` with a Haiku entry
+     * (no `supportsAutoMode`), Opus + Sonnet entries with `supportsAutoMode:
+     * true`, and seed `availableModes` so it currently includes `auto`. This
+     * exercises the per-model recomputation done by `applyConfigOptionValue`
+     * on a model switch.
+     */
+    function setupHaikuOpusSession(currentModeId: string = "default") {
+      const session = (agent as unknown as { sessions: Record<string, any> }).sessions[SESSION_ID];
+      session.modelInfos = [
+        {
+          value: "claude-opus-4-5",
+          displayName: "Claude Opus",
+          description: "Most capable",
+          supportsEffort: true,
+          supportedEffortLevels: ["low", "medium", "high"],
+          supportsAutoMode: true,
+        },
+        {
+          value: "claude-sonnet-4-5",
+          displayName: "Claude Sonnet",
+          description: "Balanced",
+          supportsEffort: true,
+          supportedEffortLevels: ["low", "medium", "high"],
+          supportsAutoMode: true,
+        },
+        {
+          value: "claude-haiku-4-5",
+          displayName: "Claude Haiku",
+          description: "Fast",
+          supportsEffort: true,
+          supportedEffortLevels: ["low", "medium", "high"],
+          // supportsAutoMode intentionally omitted
+        },
+      ];
+      session.models = {
+        currentModelId: "claude-opus-4-5",
+        availableModels: [
+          { modelId: "claude-opus-4-5", name: "Claude Opus", description: "Most capable" },
+          { modelId: "claude-sonnet-4-5", name: "Claude Sonnet", description: "Balanced" },
+          { modelId: "claude-haiku-4-5", name: "Claude Haiku", description: "Fast" },
+        ],
+      };
+      session.modes = {
+        currentModeId,
+        availableModes: [
+          {
+            id: "auto",
+            name: "Auto",
+            description: "Use a model classifier to approve/deny permission prompts",
+          },
+          {
+            id: "default",
+            name: "Default",
+            description: "Standard behavior, prompts for dangerous operations",
+          },
+          {
+            id: "acceptEdits",
+            name: "Accept Edits",
+            description: "Auto-accept file edit operations",
+          },
+          { id: "plan", name: "Plan Mode", description: "Planning mode" },
+          {
+            id: "dontAsk",
+            name: "Don't Ask",
+            description: "Don't prompt for permissions, deny if not pre-approved",
+          },
+        ],
+      };
+      // Reflect the seeded availableModes/availableModels in configOptions so
+      // the pre-state matches what `createSession` would have produced for
+      // Opus, and `setSessionConfigOption` validation can accept the seeded
+      // model ids (notably the new Haiku entry).
+      session.configOptions = session.configOptions.map((o: any) => {
+        if (o.id === "mode") {
+          return {
+            ...o,
+            currentValue: currentModeId,
+            options: session.modes.availableModes.map((m: any) => ({
+              value: m.id,
+              name: m.name,
+              description: m.description,
+            })),
+          };
+        }
+        if (o.id === "model") {
+          return {
+            ...o,
+            currentValue: session.models.currentModelId,
+            options: session.models.availableModels.map((m: any) => ({
+              value: m.modelId,
+              name: m.name,
+              description: m.description,
+            })),
+          };
+        }
+        return o;
+      });
+      return session;
+    }
+
+    beforeEach(() => {
+      populateSession();
+    });
+
+    it("drops `auto` from available modes when switching to Haiku", async () => {
+      setupHaikuOpusSession("default");
+
+      await agent.unstable_setSessionModel({
+        sessionId: SESSION_ID,
+        modelId: "claude-haiku-4-5",
+      });
+
+      const configUpdate = sessionUpdates.find(
+        (n) => n.update.sessionUpdate === "config_option_update",
+      );
+      expect(configUpdate).toBeDefined();
+      const modeOption = (configUpdate?.update as any).configOptions.find(
+        (o: any) => o.id === "mode",
+      );
+      expect(modeOption).toBeDefined();
+      const modeValues = modeOption.options.map((o: any) => o.value);
+      expect(modeValues).not.toContain("auto");
+      expect(modeValues).toEqual(
+        expect.arrayContaining(["default", "acceptEdits", "plan", "dontAsk"]),
+      );
+    });
+
+    it("clamps to `default` and emits current_mode_update when Opus(auto) → Haiku", async () => {
+      setupHaikuOpusSession("auto");
+
+      await agent.unstable_setSessionModel({
+        sessionId: SESSION_ID,
+        modelId: "claude-haiku-4-5",
+      });
+
+      // SDK was synced to "default".
+      expect(setPermissionModeSpy).toHaveBeenCalledWith("default");
+
+      // current_mode_update was emitted before config_option_update so a
+      // client applying notifications in order observes the mode change
+      // before re-rendering the config-option list.
+      const modeUpdateIdx = sessionUpdates.findIndex(
+        (n) => n.update.sessionUpdate === "current_mode_update",
+      );
+      const configUpdateIdx = sessionUpdates.findIndex(
+        (n) => n.update.sessionUpdate === "config_option_update",
+      );
+      expect(modeUpdateIdx).toBeGreaterThanOrEqual(0);
+      expect(configUpdateIdx).toBeGreaterThanOrEqual(0);
+      expect(modeUpdateIdx).toBeLessThan(configUpdateIdx);
+      expect((sessionUpdates[modeUpdateIdx].update as any).currentModeId).toBe("default");
+
+      // configOptions reflect the clamped mode.
+      const modeOption = (sessionUpdates[configUpdateIdx].update as any).configOptions.find(
+        (o: any) => o.id === "mode",
+      );
+      expect(modeOption.currentValue).toBe("default");
+    });
+
+    it("re-adds `auto` when switching from Haiku back to Opus", async () => {
+      const session = setupHaikuOpusSession("default");
+      // Pretend Haiku is the current model with no `auto`.
+      session.models.currentModelId = "claude-haiku-4-5";
+      session.modes.availableModes = session.modes.availableModes.filter(
+        (m: any) => m.id !== "auto",
+      );
+      const modeOpt = session.configOptions.find((o: any) => o.id === "mode");
+      modeOpt.options = session.modes.availableModes.map((m: any) => ({
+        value: m.id,
+        name: m.name,
+        description: m.description,
+      }));
+
+      await agent.unstable_setSessionModel({
+        sessionId: SESSION_ID,
+        modelId: "claude-opus-4-5",
+      });
+
+      const configUpdate = sessionUpdates.find(
+        (n) => n.update.sessionUpdate === "config_option_update",
+      );
+      expect(configUpdate).toBeDefined();
+      const modeOption = (configUpdate?.update as any).configOptions.find(
+        (o: any) => o.id === "mode",
+      );
+      const modeValues = modeOption.options.map((o: any) => o.value);
+      expect(modeValues).toContain("auto");
+
+      // The current mode ("default") is still valid on Opus, so no
+      // current_mode_update should have been emitted by the model switch.
+      const modeUpdates = sessionUpdates.filter(
+        (n) => n.update.sessionUpdate === "current_mode_update",
+      );
+      expect(modeUpdates).toHaveLength(0);
+    });
+
+    it("preserves the current mode when it remains valid after a model switch", async () => {
+      setupHaikuOpusSession("plan");
+
+      await agent.unstable_setSessionModel({
+        sessionId: SESSION_ID,
+        modelId: "claude-haiku-4-5",
+      });
+
+      // `plan` is in availableModes for both Opus and Haiku, so no clamp.
+      expect(setPermissionModeSpy).not.toHaveBeenCalledWith("default");
+
+      const modeUpdates = sessionUpdates.filter(
+        (n) => n.update.sessionUpdate === "current_mode_update",
+      );
+      expect(modeUpdates).toHaveLength(0);
+
+      const configUpdate = sessionUpdates.find(
+        (n) => n.update.sessionUpdate === "config_option_update",
+      );
+      const modeOption = (configUpdate?.update as any).configOptions.find(
+        (o: any) => o.id === "mode",
+      );
+      expect(modeOption.currentValue).toBe("plan");
+    });
+
+    it("clamps mode and emits current_mode_update via setSessionConfigOption(model)", async () => {
+      // Mirrors the unstable_setSessionModel(auto → Haiku) test, but goes
+      // through the request/response API. The `current_mode_update` side
+      // effect must still fire so clients learn about the clamp regardless of
+      // which entry point triggered the model switch.
+      setupHaikuOpusSession("auto");
+
+      const response = await agent.setSessionConfigOption({
+        sessionId: SESSION_ID,
+        configId: "model",
+        value: "claude-haiku-4-5",
+      });
+
+      expect(setPermissionModeSpy).toHaveBeenCalledWith("default");
+
+      const modeUpdates = sessionUpdates.filter(
+        (n) => n.update.sessionUpdate === "current_mode_update",
+      );
+      expect(modeUpdates).toHaveLength(1);
+      expect((modeUpdates[0].update as any).currentModeId).toBe("default");
+
+      // setSessionConfigOption is a request/response API: it returns the new
+      // configOptions in the response rather than emitting a
+      // config_option_update notification.
+      const configUpdates = sessionUpdates.filter(
+        (n) => n.update.sessionUpdate === "config_option_update",
+      );
+      expect(configUpdates).toHaveLength(0);
+
+      const modeOption = response.configOptions.find((o: any) => o.id === "mode");
+      expect(modeOption).toBeDefined();
+      expect((modeOption as any).currentValue).toBe("default");
+      expect((modeOption as any).options.map((o: any) => o.value)).not.toContain("auto");
+    });
+
+    it("rejects direct setSessionMode to `auto` when the active model does not offer it", async () => {
+      const session = setupHaikuOpusSession("default");
+      session.models.currentModelId = "claude-haiku-4-5";
+      session.modes.availableModes = session.modes.availableModes.filter(
+        (mode: any) => mode.id !== "auto",
+      );
+
+      await expect(agent.setSessionMode({ sessionId: SESSION_ID, modeId: "auto" })).rejects.toThrow(
+        "Mode auto is not available in this session",
+      );
+
+      expect(setPermissionModeSpy).not.toHaveBeenCalledWith("auto");
+      expect(sessionUpdates).toHaveLength(0);
+    });
+  });
+
+  describe("ExitPlanMode permission options filtered by availableModes", () => {
+    let capturedPermissionRequest: any;
+    let permissionResponse: any;
+
+    beforeEach(() => {
+      capturedPermissionRequest = null;
+      permissionResponse = { outcome: { outcome: "cancelled" } };
+      // Replace the default mock client with one that captures the
+      // requestPermission call so we can assert on the offered options.
+      (agent as any).client = {
+        sessionUpdate: async (notification: SessionNotification) => {
+          sessionUpdates.push(notification);
+        },
+        requestPermission: async (params: any) => {
+          capturedPermissionRequest = params;
+          return permissionResponse;
+        },
+        readTextFile: async () => ({ content: "" }),
+        writeTextFile: async () => ({}),
+      };
+      populateSession();
+    });
+
+    it("omits the `auto` option on a model without supportsAutoMode", async () => {
+      const session = (agent as unknown as { sessions: Record<string, any> }).sessions[SESSION_ID];
+      // Haiku-shaped session: availableModes does NOT include `auto`.
+      session.modes = {
+        currentModeId: "plan",
+        availableModes: [
+          { id: "default", name: "Default", description: "Standard" },
+          { id: "acceptEdits", name: "Accept Edits", description: "Auto-accept edits" },
+          { id: "plan", name: "Plan Mode", description: "Planning mode" },
+          { id: "dontAsk", name: "Don't Ask", description: "Deny if not pre-approved" },
+        ],
+      };
+
+      const canUseTool = (agent as any).canUseTool(SESSION_ID);
+      const signal = new AbortController().signal;
+      try {
+        await canUseTool(
+          "ExitPlanMode",
+          { plan: "do stuff" },
+          { signal, suggestions: undefined, toolUseID: "toolu_1" },
+        );
+      } catch {
+        // The mock client returns `cancelled`, which makes canUseTool throw.
+        // We only care about the captured requestPermission options.
+      }
+
+      expect(capturedPermissionRequest).not.toBeNull();
+      const optionIds = capturedPermissionRequest.options.map((o: any) => o.optionId);
+      expect(optionIds).not.toContain("auto");
+      expect(optionIds).toEqual(expect.arrayContaining(["default", "acceptEdits", "plan"]));
+    });
+
+    it("denies a selected `auto` option if the client did not receive that option", async () => {
+      const session = (agent as unknown as { sessions: Record<string, any> }).sessions[SESSION_ID];
+      session.modes = {
+        currentModeId: "plan",
+        availableModes: [
+          { id: "default", name: "Default", description: "Standard" },
+          { id: "acceptEdits", name: "Accept Edits", description: "Auto-accept edits" },
+          { id: "plan", name: "Plan Mode", description: "Planning mode" },
+          { id: "dontAsk", name: "Don't Ask", description: "Deny if not pre-approved" },
+        ],
+      };
+      permissionResponse = { outcome: { outcome: "selected", optionId: "auto" } };
+
+      const canUseTool = (agent as any).canUseTool(SESSION_ID);
+      const result = await canUseTool(
+        "ExitPlanMode",
+        { plan: "do stuff" },
+        { signal: new AbortController().signal, suggestions: undefined, toolUseID: "toolu_2" },
+      );
+
+      expect(capturedPermissionRequest).not.toBeNull();
+      const optionIds = capturedPermissionRequest.options.map((o: any) => o.optionId);
+      expect(optionIds).not.toContain("auto");
+      expect(result.behavior).toBe("deny");
+      expect(sessionUpdates).toHaveLength(0);
+    });
+
+    it("includes the `auto` option on a model with supportsAutoMode", async () => {
+      const session = (agent as unknown as { sessions: Record<string, any> }).sessions[SESSION_ID];
+      session.modes = {
+        currentModeId: "plan",
+        availableModes: [
+          { id: "auto", name: "Auto", description: "Use a model classifier" },
+          { id: "default", name: "Default", description: "Standard" },
+          { id: "acceptEdits", name: "Accept Edits", description: "Auto-accept edits" },
+          { id: "plan", name: "Plan Mode", description: "Planning mode" },
+          { id: "dontAsk", name: "Don't Ask", description: "Deny if not pre-approved" },
+        ],
+      };
+
+      const canUseTool = (agent as any).canUseTool(SESSION_ID);
+      const signal = new AbortController().signal;
+      try {
+        await canUseTool(
+          "ExitPlanMode",
+          { plan: "do stuff" },
+          { signal, suggestions: undefined, toolUseID: "toolu_3" },
+        );
+      } catch {
+        // mock returns cancelled
+      }
+
+      expect(capturedPermissionRequest).not.toBeNull();
+      const optionIds = capturedPermissionRequest.options.map((o: any) => o.optionId);
+      expect(optionIds).toContain("auto");
+    });
+  });
 });