refactor(sse): route executor lookup through ExecutorRegistry (R0.3)

Adds open-sse/executors/registry.ts (Map-based registry mirroring
translator/registry.ts): the built-in table in executors/index.ts stays
declarative, every entry is registered at module load, and
getExecutor()/hasSpecializedExecutor() resolve through the registry.
DefaultExecutor fallback, its memoization, and the cloud-agent (#6699) /
search-provider (#10274) guards are unchanged.

Also fixes a latent lookup leak: the old object-literal lookup treated
Object.prototype names (constructor, toString, ...) as specialized
executors; the Map registry resolves them to the DefaultExecutor
fallback like any unknown provider.

Parity proof: executor-map golden (137 entries, byte-identical
before/after), check:known-symbols green, 1018 tests across the 65
executor test files green. Docs: OPEN_SSE_ARCHITECTURE factory section
corrected (it claimed generation from providerRegistry).

Refs #3501

docs/frameworks/OPEN_SSE_ARCHITECTURE.md

@@ -368,7 +368,7 @@ const result = await executor.execute({
 });
 ````
 
-The factory is generated from `config/providerRegistry.ts` which lists all 338 providers and their executor class.
+Resolution goes through the `ExecutorRegistry` (`executors/registry.ts`): every specialized executor is declared in the built-in table of `executors/index.ts` and registered via `registerExecutor(alias, instance)` at module load; `getExecutor()` consults the registry and falls back to a memoized `DefaultExecutor` for any provider without a specialized entry. The full alias → executor mapping is characterized by the golden test `tests/unit/executor-map-golden.test.ts`.
 
 ---
 

open-sse/executors/index.ts

@@ -1,4 +1,9 @@
 import { SEARCH_PROVIDERS } from "../config/searchRegistry.ts";
+import {
+  registerExecutor,
+  getRegisteredExecutor,
+  hasRegisteredExecutor,
+} from "./registry.ts";
 import { AntigravityExecutor } from "./antigravity.ts";
 import { GithubExecutor } from "./github.ts";
 import { GheCopilotExecutor } from "./ghe-copilot.ts";
@@ -78,6 +83,12 @@ import { XaiExecutor } from "./xai.ts";
 import { PromptQlExecutor } from "./promptql.ts";
 import { ConolWebExecutor } from "./conol-web.ts";
 
+// R0.3 — declarative built-in table. The object literal stays as the single
+// place built-ins are declared (compile-time duplicate-key safety; the
+// check:known-symbols gate parses this literal from source), but lookup goes
+// through the ExecutorRegistry (./registry.ts): every entry is registered at
+// module load below, and getExecutor()/hasSpecializedExecutor() consult the
+// registry — the literal is never read at request time.
 const executors = {
   antigravity: new AntigravityExecutor(),
   agy: new AntigravityExecutor(),
@@ -221,6 +232,13 @@ const executors = {
   cnl: new ConolWebExecutor(), // Alias
 };
 
+// Bootstrap: register every built-in in the ExecutorRegistry. registerExecutor
+// throws on duplicates, so an alias collision fails at module load, exactly as
+// loudly as a duplicate object key would have failed at lint time.
+for (const [alias, executor] of Object.entries(executors)) {
+  registerExecutor(alias, executor);
+}
+
 const defaultCache = new Map();
 
 // #6699 — providers that exist ONLY as Cloud Agent task-API entries
@@ -246,7 +264,8 @@ const CHAT_UNSUPPORTED_CLOUD_AGENT_PROVIDERS = new Set(["jules"]);
 const CHAT_UNSUPPORTED_SEARCH_PROVIDERS = new Set(Object.keys(SEARCH_PROVIDERS));
 
 export function getExecutor(provider) {
-  if (executors[provider]) return executors[provider];
+  const registered = getRegisteredExecutor(provider);
+  if (registered) return registered;
   if (CHAT_UNSUPPORTED_CLOUD_AGENT_PROVIDERS.has(provider)) {
     const err = new Error(
       `Provider "${provider}" is a cloud-agent provider and does not support direct chat completions; use the Cloud Agents task API instead.`
@@ -266,9 +285,11 @@ export function getExecutor(provider) {
 }
 
 export function hasSpecializedExecutor(provider) {
-  return !!executors[provider];
+  return hasRegisteredExecutor(provider);
 }
 
+export { registerExecutor, listExecutorAliases } from "./registry.ts";
+
 export { BaseExecutor } from "./base.ts";
 export { AntigravityExecutor } from "./antigravity.ts";
 export { GithubExecutor } from "./github.ts";

open-sse/executors/registry.ts

@@ -0,0 +1,38 @@
+import type { BaseExecutor } from "./base.ts";
+
+// R0.3 — ExecutorRegistry: runtime registry for provider executors, mirroring
+// open-sse/translator/registry.ts. Built-ins register at module load from
+// executors/index.ts; getExecutor() resolves through this map instead of a
+// hard-coded object literal. This is the seam the v4 plan (M1.6
+// host.registerProvider) extends — today the surface is internal-only.
+//
+// The alias → executor mapping is characterized by
+// tests/unit/executor-map-golden.test.ts (tests/snapshots/executors/): any
+// change to keys, classes or instance sharing shows up as a golden diff.
+
+const registry = new Map<string, BaseExecutor>();
+
+/**
+ * Register an executor under an alias. Aliases are unique: registering the
+ * same alias twice throws, preserving the guarantee the old object literal
+ * gave at compile time (duplicate keys were impossible).
+ */
+export function registerExecutor(alias: string, executor: BaseExecutor): void {
+  if (registry.has(alias)) {
+    throw new Error(`executor alias already registered: "${alias}"`);
+  }
+  registry.set(alias, executor);
+}
+
+export function getRegisteredExecutor(alias: string): BaseExecutor | undefined {
+  return registry.get(alias);
+}
+
+export function hasRegisteredExecutor(alias: string): boolean {
+  return registry.has(alias);
+}
+
+/** All registered aliases, in registration order. */
+export function listExecutorAliases(): string[] {
+  return [...registry.keys()];
+}

tests/unit/executor-registry.test.ts

@@ -0,0 +1,57 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+// R0.3 — unit tests for the ExecutorRegistry seam itself (registration
+// semantics + wiring of the built-ins). Behavior parity of the full map is
+// covered separately by tests/unit/executor-map-golden.test.ts.
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-executor-registry-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const { registerExecutor, getRegisteredExecutor, hasRegisteredExecutor, listExecutorAliases } =
+  await import("../../open-sse/executors/registry.ts");
+const { getExecutor, hasSpecializedExecutor, BaseExecutor, DefaultExecutor } = await import(
+  "../../open-sse/executors/index.ts"
+);
+
+test.after(() => {
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+test("built-ins are registered at module load and resolve through the registry", () => {
+  const aliases = listExecutorAliases();
+  assert.ok(aliases.length >= 100, `expected the built-in table, got ${aliases.length} aliases`);
+  for (const alias of ["antigravity", "kiro", "glm", "9router", "conol-web"]) {
+    assert.ok(hasRegisteredExecutor(alias), `missing built-in: ${alias}`);
+    assert.equal(getExecutor(alias), getRegisteredExecutor(alias));
+    assert.ok(getExecutor(alias) instanceof BaseExecutor);
+  }
+});
+
+test("registerExecutor throws on duplicate alias", () => {
+  assert.throws(() => registerExecutor("kiro", getRegisteredExecutor("kiro")!), {
+    message: /already registered: "kiro"/,
+  });
+});
+
+test("registering a new alias makes it resolvable via getExecutor and hasSpecializedExecutor", () => {
+  const alias = "registry-test-provider";
+  assert.equal(hasSpecializedExecutor(alias), false);
+  const instance = new DefaultExecutor(alias);
+  registerExecutor(alias, instance);
+  assert.equal(hasSpecializedExecutor(alias), true);
+  assert.equal(getExecutor(alias), instance);
+});
+
+test("registry lookup is exact — Object.prototype names are not executors", () => {
+  // The old object-literal lookup (`executors[provider]`) leaked prototype
+  // members: getExecutor("constructor") returned Object's constructor. The Map
+  // registry must treat these as unknown providers (DefaultExecutor fallback).
+  for (const name of ["constructor", "toString", "hasOwnProperty", "__proto__"]) {
+    assert.equal(hasSpecializedExecutor(name), false, name);
+    assert.ok(getExecutor(name) instanceof DefaultExecutor, name);
+  }
+});