fix(agent): default agent selection in acp and headless mode #8678

assagman · 2026-01-15T14:15:11Z

Summary

Make ACP and headless mode respect default_agent config and properly handle agent modes and visibilities. Previously, subagents and hidden agents could be incorrectly selected as the default agent.

Fixes #8680

Changes

Filter out subagents (mode === "subagent") from defaultAgent candidates
Filter out hidden agents (hidden === true) from defaultAgent candidates
4 different errors introduced:
- default agent "${cfg.default_agent}" not found
- default agent "${cfg.default_agent}" is a subagent
- default agent "${cfg.default_agent}" is hidden
- no primary visible agent found
Add 7 test cases for defaultAgent selection logic
Persist default mode in session manager during ACP session init

Breaking Changes

None

Testing

Added unit tests covering agent selection cases

github-actions · 2026-01-15T14:15:29Z

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

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Open an issue describing the bug/feature (if one doesn't exist)
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github-actions · 2026-01-15T14:15:50Z

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found the following potentially related PRs:

Related PRs:

fix(tui): guard default agent selection #7796 - fix(tui): guard default agent selection
- Directly related to default agent selection logic, though focused on TUI
Add default variant config per agent #7140 - Add default variant config per agent
- Related to default configuration per agent, though focused on variants rather than mode/visibility filtering
feat(agent): add subagents config for per-agent task tool filtering #7271 - feat(agent): add subagents config for per-agent task tool filtering
- Handles subagent configuration which is mentioned in this PR's filtering logic
fix(tui): handle undefined agent during login/bootstrap transition #7940 - fix(tui): handle undefined agent during login/bootstrap transition
- Related to agent selection edge cases during transitions
fix(acp): persist session state to disk and add isReplay metadata #6563 - fix(acp): persist session state to disk and add isReplay metadata
- Related to ACP mode mentioned in this PR, though focused on session persistence

These are not direct duplicates of PR #8678, but they address related aspects of agent selection, configuration, and mode handling. The most closely related is #7796 which also deals with guarding default agent selection.

Copilot

Pull request overview

This pull request fixes default agent selection in ACP and headless modes to properly respect the default_agent configuration while filtering out unsuitable agents (subagents and hidden agents).

Changes:

Modified Agent.defaultAgent() to filter out subagents and hidden agents from default selection
Added logic to persist the default agent mode in ACP session initialization
Added 7 comprehensive unit tests covering various default agent selection scenarios

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/opencode/src/agent/agent.ts	Updated `defaultAgent()` function with proper filtering logic for subagents and hidden agents with appropriate fallback behavior
packages/opencode/src/acp/agent.ts	Added `setMode()` call to persist default agent mode during ACP session initialization
packages/opencode/test/agent/agent.test.ts	Added 7 test cases covering default agent selection including config respect, subagent filtering, hidden agent filtering, non-existent agents, and disabled build scenarios

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…ction Signed-off-by: assagman <[email protected]>

Signed-off-by: assagman <[email protected]>

Previously used 3-step fallback (primary -> visible -> build). Now uses single check: find primary+visible OR hardcoded 'build'. Same behavior, cleaner implementation. Signed-off-by: assagman <[email protected]>

rekram1-node · 2026-01-15T17:41:35Z

packages/opencode/src/agent/agent.ts

  export async function defaultAgent() {
-    return state().then((x) => Object.keys(x)[0])
+    const agents = await list()
+    const primaryVisible = agents.find((a) => a.mode !== "subagent" && a.hidden !== true)
+    return primaryVisible?.name || "build"


I think we should prolly throw an error if no primary agent is available... Thoughts?

Yes, I'm currently thinking about it. Maybe you're right.

TUI throws unhandled exception here: https://github.com/anomalyco/opencode/blob/dev/packages/opencode/src/cli/cmd/tui/context/local.tsx#L41-L41

(when no primary visible agent found)

Hey @rekram1-node , I've updated the logic as throwing errors for invalid cases:

cfg.default_agent is set:
a. cfg.default_agent is not found in state
b. cfg.default_agent is a subagent
c. cfg.default_agent is hidden

cfg.default_agent is not set and all of them either subagent or hidden -> no primary visible agent found

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

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packages/opencode/test/agent/agent.test.ts

Users now see specific error messages explaining why their configured default_agent cannot be used (not found, is subagent, or is hidden) instead of silently falling back to a different agent. Signed-off-by: assagman <[email protected]>

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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rekram1-node · 2026-01-15T22:47:30Z

/review

github-actions · 2026-01-15T22:48:31Z

lgtm

Copilot AI review requested due to automatic review settings January 15, 2026 14:15

github-actions bot added the needs:issue label Jan 15, 2026

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assagman mentioned this pull request Jan 15, 2026

ACP and headless mode does not respect default agent definition #8680

Closed

assagman added 3 commits January 15, 2026 19:49

fix(agent): filter subagents and hidden agents from defaultAgent sele…

7b12bc5

…ction Signed-off-by: assagman <[email protected]>

fix(acp): persist default mode on session init

94ff788

Signed-off-by: assagman <[email protected]>

test(agent): add coverage for defaultAgent selection logic

9dc3746

Signed-off-by: assagman <[email protected]>

assagman force-pushed the fix/default-agent-selection branch from 8d1a6ef to 9dc3746 Compare January 15, 2026 16:50

core: simplify defaultAgent to single fallback path

d558873

Previously used 3-step fallback (primary -> visible -> build). Now uses single check: find primary+visible OR hardcoded 'build'. Same behavior, cleaner implementation. Signed-off-by: assagman <[email protected]>

rekram1-node reviewed Jan 15, 2026

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assagman changed the title ~~fix(agent): default agent selection in acp and headless modes~~ fix(agent): default agent selection in acp and headless mode Jan 15, 2026

assagman requested review from Copilot and rekram1-node January 15, 2026 19:02

Copilot started reviewing on behalf of assagman January 15, 2026 19:03 View session

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assagman force-pushed the fix/default-agent-selection branch from b1ba56d to e6a6e61 Compare January 15, 2026 19:19

assagman requested a review from Copilot January 15, 2026 19:19

Copilot started reviewing on behalf of assagman January 15, 2026 19:19 View session

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rekram1-node merged commit 81983d4 into anomalyco:dev Jan 15, 2026
8 of 9 checks passed

assagman deleted the fix/default-agent-selection branch January 15, 2026 23:10

fix(agent): default agent selection in acp and headless mode #8678

fix(agent): default agent selection in acp and headless mode #8678

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assagman commented Jan 15, 2026 •

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