From caf32c33e3119f8060c91b35bd13923895f75cd4 Mon Sep 17 00:00:00 2001
From: Drew Stone <drewstone329@gmail.com>
Date: Mon, 19 Oct 2026 19:10:10 -0600
Subject: [PATCH] feat(opencode): declare toolCallSpans on /v1/capabilities so
 agent-runtime can bound a silent model call

#266 made opencode report each tool call at its start; its finished part already
carried the outcome. agent-runtime (#1885) runs modelSilenceMs only on a route that
declares toolCallSpans: true, and no backend declared it, so the bound was off on
every route. The opencode backend now declares it and /v1/capabilities serves it.
---
 src/backends/opencode.ts        | 3 +++
 src/backends/types.ts           | 6 ++++++
 src/sessions/retained.ts        | 9 ++++++---
 tests/retained-sessions.test.ts | 8 ++++++++
 4 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/backends/opencode.ts b/src/backends/opencode.ts
index ecbc5c4..2386fbf 100644
--- a/src/backends/opencode.ts
+++ b/src/backends/opencode.ts
@@ -57,6 +57,9 @@ export interface OpencodeBackendOptions {
 export class OpencodeBackend implements Backend {
   readonly name = 'opencode'
   readonly defaultExecutionTimeoutMs: number
+  // The signal plugin reports a call at its start; it is installed in the turn's private config
+  // directory, which every turn with an AgentProfile has (agent-runtime always sends one).
+  readonly toolCallSpans = true
   private readonly spawner: Spawner
   constructor(private readonly opts: OpencodeBackendOptions) {
     this.defaultExecutionTimeoutMs = opts.timeoutMs
diff --git a/src/backends/types.ts b/src/backends/types.ts
index 87797df..17bed9d 100644
--- a/src/backends/types.ts
+++ b/src/backends/types.ts
@@ -603,6 +603,12 @@ export interface Backend {
   readonly name: string
   /** Operator-selected fallback used only when `execution.timeoutMs` is absent. Zero/absent means no deadline. */
   readonly defaultExecutionTimeoutMs?: number
+  /**
+   * The stream reports each tool call when it starts and its outcome when it ends, so a caller can
+   * tell a silent model from a running tool. Served as `toolCallSpans` on `/v1/capabilities`;
+   * agent-runtime runs `modelSilenceMs` only on a route that declares it.
+   */
+  readonly toolCallSpans?: boolean
 
   /** Does this backend want to handle requests for `model`? */
   matches(model: string): boolean
diff --git a/src/sessions/retained.ts b/src/sessions/retained.ts
index 8244df8..b654c38 100644
--- a/src/sessions/retained.ts
+++ b/src/sessions/retained.ts
@@ -146,14 +146,17 @@ export class RetainedSessionService {
     return parseNativeContinuation(value)
   }
 
-  async capabilities(model: string, signal?: AbortSignal): Promise<AgentEnvironmentCapabilities> {
-    const { capabilities } = await readyBackendCapabilities({
+  async capabilities(
+    model: string,
+    signal?: AbortSignal,
+  ): Promise<AgentEnvironmentCapabilities & { toolCallSpans?: true }> {
+    const { backend, capabilities } = await readyBackendCapabilities({
       registry: this.registry,
       model,
       healthProbeTimeoutMs: this.healthProbeTimeoutMs,
       signal,
     })
-    return capabilities
+    return backend.toolCallSpans ? { ...capabilities, toolCallSpans: true } : capabilities
   }
 
   async create(input: RetainedCreateInput, signal?: AbortSignal): Promise<RetainedSessionView> {
diff --git a/tests/retained-sessions.test.ts b/tests/retained-sessions.test.ts
index 03ed6db..37eb87d 100644
--- a/tests/retained-sessions.test.ts
+++ b/tests/retained-sessions.test.ts
@@ -1077,6 +1077,14 @@ describe('retained Agent Interface sessions', () => {
     })
     expect(capabilities).not.toHaveProperty('nativeContinuation')
     expect(capabilities).not.toHaveProperty('interactions')
+    expect(capabilities).not.toHaveProperty('toolCallSpans')
+  })
+
+  it('declares toolCallSpans only for a backend whose stream reports a call at its start and end', async () => {
+    fixture = setup(Object.assign(new OneShotBackend('opencode'), { toolCallSpans: true }))
+    const response = await fixture.app.request('/v1/capabilities?model=opencode%2Ftest')
+    expect(response.status).toBe(200)
+    expect(await json(response)).toMatchObject({ toolCallSpans: true, streaming: { live: true } })
   })
 
   it('refuses retained capability discovery and creation until native health is ready', async () => {