coder(providers): v2.3 provider-lifecycle phase 3 — generic ACP dispatch

ACP dispatch now spawns from the resolved registry's launch spec instead of a hardcoded per-name switch. acp-spawn.ts gains resolveLaunchSpec(resolved, installPath): launchCommand (config override / custom-ACP command) wins, else the kept resolveAcpSpawnArgs switch is the built-in fallback. acp-dispatch.ts spawns spec.binary/spec.args with env { ...process.env, ...spec.env }; dispatcher.ts loads the resolved def by task.agent and passes it through. Config-defined custom ACP providers dispatch with no new switch case. Built-in dispatch (opencode/goose/qwen) is byte-identical to pre-v2.3 — proven by a regression test (opencode->['acp'], goose->['acp'], qwen->['--acp'], binary=installPath ?? id, empty env -> plain process.env). Deliberate deviation from design's !installPath->null: the installPath ?? id fallback is preserved. setSessionMode/permission/streaming and the dispatcher poll/NOTIFY/running-guard untouched. 7 new acp-spawn.test.ts cases. No routes/UI (Phase 4+).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/coder/src/services/acp-spawn.ts

@@ -1,5 +1,9 @@
+import type { ResolvedProviderDef } from './provider-config-registry.js';
+
 /**
- * Resolve ACP spawn argv per provider (host-probe verified 2026-05-25).
+ * Resolve ACP spawn argv per built-in provider (host-probe verified 2026-05-25).
+ * Source of truth for built-in default argv — resolveLaunchSpec wraps these; it
+ * does NOT replace them.
  */
 export function resolveAcpSpawnArgs(agent: string): string[] | null {
   switch (agent) {
@@ -13,6 +17,34 @@ export function resolveAcpSpawnArgs(agent: string): string[] | null {
   }
 }
 
+/**
+ * v2.3 phase 3: resolve the launch spec for an ACP dispatch (design.md §5.1).
+ * Consults the resolved registry's launchCommand (config override or custom-ACP
+ * entry) first; otherwise falls back to the built-in default argv above.
+ *
+ * Byte-identical to pre-v2.3 for built-ins with no override: binary is
+ * `installPath ?? id` and args come from resolveAcpSpawnArgs — exactly the
+ * `binary = installPath ?? agent` + `resolveAcpSpawnArgs(agent)` the dispatcher
+ * used before. (Deliberate deviation from design §5.1's `!installPath → null`:
+ * the old path spawned the bare agent name when install_path was missing, so we
+ * preserve the `?? id` fallback rather than fail.)
+ */
+export function resolveLaunchSpec(
+  resolved: ResolvedProviderDef,
+  installPath: string | null,
+): { binary: string; args: string[]; env?: Record<string, string> } | null {
+  if (resolved.launchCommand) {
+    return {
+      binary: resolved.launchCommand[0],
+      args: resolved.launchCommand.slice(1),
+      env: resolved.env,
+    };
+  }
+  const args = resolveAcpSpawnArgs(resolved.id);
+  if (!args) return null;
+  return { binary: installPath ?? resolved.id, args, env: resolved.env };
+}
+
 export function resolveAcpProbeBinaries(agent: string): string[] {
   return [agent];
 }