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Stop advertising fork for acp-cursor and acp-grok #2150

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Merged
SawyerHood merged 1 commit into from
Aug 21, 2026
Merged

Stop advertising fork for acp-cursor and acp-grok #2150

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30 changes: 29 additions & 1 deletion apps/server/test/services/plugins/first-party-provider-plugins.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "Codex",
supportsThreadArchive: true,
supportsThreadRename: true,
fork: "checkpoint",
supportsManualCompaction: true,
supportsUsage: true,
visibility: "always",
Expand All @@ -38,6 +39,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "Claude Code",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "checkpoint",
supportsManualCompaction: true,
supportsUsage: true,
visibility: "always",
Expand All @@ -50,6 +52,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "Pi",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "checkpoint",
supportsManualCompaction: true,
supportsUsage: false,
visibility: "always",
Expand All @@ -62,6 +65,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "Cursor",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "none",
supportsManualCompaction: false,
supportsUsage: true,
visibility: "always",
Expand All @@ -74,6 +78,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "opencode",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "tip",
supportsManualCompaction: true,
supportsUsage: false,
visibility: "installed",
Expand All @@ -86,6 +91,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "omp",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "tip",
supportsManualCompaction: false,
supportsUsage: false,
visibility: "installed",
Expand All @@ -98,6 +104,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "Grok Build",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "none",
supportsManualCompaction: false,
supportsUsage: false,
visibility: "installed",
Expand All @@ -110,6 +117,7 @@ const FIRST_PARTY_PROVIDER_DECLARATIONS = [
displayName: "Hermes Agent",
supportsThreadArchive: false,
supportsThreadRename: false,
fork: "tip",
supportsManualCompaction: false,
supportsUsage: false,
visibility: "installed",
Expand Down Expand Up @@ -191,6 +199,16 @@ describe("first-party provider plugins", () => {
expect(registry.supportsManualCompaction(plugin.providerId)).toBe(
plugin.supportsManualCompaction,
);
// Fork is declared per agent, not per tier: the ACP bridge refuses
// `session/fork` for agents whose `initialize` reply does not
// advertise it (cursor-agent, grok), so a declaration above what the
// agent answers makes POST /threads/fork create a thread that dies
// on start (#1833). The declaration is the server's fork gate and
// the app's fork affordance, so it must match the agent.
expect(registration.serverCapabilities.fork, label).toBe(plugin.fork);
expect(registry.supportsFork(plugin.providerId), label).toBe(
plugin.fork !== "none",
);
expect(registration.info.experimental_providerUsage, label).toBe(
plugin.supportsUsage,
);
Expand All @@ -207,6 +225,15 @@ describe("first-party provider plugins", () => {
expect(infos.map((info) => info.logoUrl)).toEqual(
ALWAYS_VISIBLE_PROVIDER_IDS.map(expectedLogoUrl),
);
// The client-facing fork flag (the app's "Fork into new thread"
// affordance) agrees with the declaration.
expect(
infos.map((info) => [info.id, info.capabilities.supportsFork]),
).toEqual(
FIRST_PARTY_PROVIDER_DECLARATIONS.filter(
(plugin) => plugin.visibility === "always",
).map((plugin) => [plugin.providerId, plugin.fork !== "none"]),
);
},
);
}, 60_000);
Expand Down Expand Up @@ -327,7 +354,8 @@ describe("first-party provider plugins", () => {
supportsServiceTier: true,
supportsNativeUserQuestion: false,
permissionModes: ["accept-edits", "full"],
supportsFork: true,
// cursor-agent does not advertise ACP session/fork (#1833).
supportsFork: false,
supportsSessionRewind: false,
},
composerActions: [skills],
Expand Down
14 changes: 14 additions & 0 deletions plugins/provider-acp/server.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,14 @@ const ACP_BASE_CAPABILITIES = {
experimental_providerInstallation: false,
supportsServiceTier: true,
supportsNativeUserQuestion: false,
// ACP session/fork clones a whole session (tip only, no checkpoint rewind),
// and it is an unstable ACP extension that not every agent implements. The
// bridge refuses `session/fork` for an agent whose `initialize` reply does
// not advertise `sessionCapabilities.fork`, but only after the server has
// already created and started the fork thread. So this declaration, which
// is the server's fork gate and the app's fork affordance, must match what
// the agent actually advertises: override it with "none" for agents that
// do not (#1833).
fork: "tip" as const,
supportsManualCompaction: false,
supportsThreadArchive: false,
Expand Down Expand Up @@ -76,6 +84,9 @@ const ACP_PROVIDERS: readonly PluginProviderDeclaration[] = [
...ACP_BASE_CAPABILITIES,
experimental_providerUsage: true,
experimental_providerInstallation: true,
// cursor-agent (2026.08.11) advertises `sessionCapabilities: { list }`
// only; no session/fork.
fork: "none",
},
composerActions: [],
},
Expand Down Expand Up @@ -166,6 +177,9 @@ const ACP_PROVIDERS: readonly PluginProviderDeclaration[] = [
},
capabilities: {
...ACP_BASE_CAPABILITIES,
// `grok agent stdio` advertises `sessionCapabilities: { list, resume,
// close }`; no session/fork.
fork: "none",
reasoningLevels: ["low", "medium", "high"],
},
composerActions: [],
Expand Down
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