feat(agent): add order field for configurable agent cycling order

[LCubero]

Issue for this PR

Closes #7372

Type of change

• New feature

What does this PR do?

Adds an optional order field (PositiveInt) to agent config so users and plugins can control Tab cycling order instead of being forced into alphabetical sort.

Currently Agent.list() sorts agents alphabetically by name (after the default agent). This breaks plugins that define multiple agents with a specific intended order. For example, oh-my-opencode defines Sisyphus → Hephaestus → Prometheus → Atlas, but alphabetical sort produces Atlas → Hephaestus → Prometheus → Sisyphus.

Sorting becomes:

1. Default agent first (unchanged)
2. By order ascending (new) — agents without order get Infinity
3. By name ascending (unchanged fallback)

Fully backward compatible — configs without order behave exactly as before.

Changes:

• packages/opencode/src/config/agent.ts: Add order to AgentSchema + KNOWN_KEYS
• packages/opencode/src/agent/agent.ts: Add order to Info schema, merge logic, and sortBy
• packages/opencode/test/agent/agent.test.ts: Add 2 tests for order field sorting

How did you verify your code works?

Two new unit tests cover the behavior:

1. Order field sorting — agents with order: 1, 2, 3 appear in that sequence after the default agent
2. Mixed ordered/unordered — agents with order appear before those without, fall back to alphabetical

The existing alphabetical sort test was renamed for clarity and still passes. Backward compatibility is verified: agents without order sort alphabetically as before.

Screenshots / recordings

N/A — no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

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

Potential Duplicate PRs Found

1. PR feat(agent): add order field for configurable agent cycling order #19127 - feat(agent): add order field for configurable agent cycling order

   • feat(agent): add order field for configurable agent cycling order #19127
   • Why related: Identical feature - adds order field for controlling agent cycling order

2. PR feat(opencode): add order field to agent config for explicit list sorting #22343 - feat(opencode): add order field to agent config for explicit list sorting

   • feat(opencode): add order field to agent config for explicit list sorting #22343
   • Why related: Same feature with slightly different naming - adds order field to agent config for list sorting control

Both of these PRs appear to address the same issue (sorting agents by configurable order field instead of alphabetically) that your PR #24691 is implementing.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍