fix(acp): list known sessions across projects on empty cwd

[Haohao-end]

Issue for this PR

Closes #33036

Type of change

• Bug fix

What does this PR do?

ACP session/list was routed through the project-scoped /session endpoint (sdk.session.list), so a request with no cwd only returned sessions for the ACP process's own project instead of every known session. Per the ACP spec, empty params must return the first page of known sessions, and cwd is an optional filter.

This switches listSessions to the cross-project listing (sdk.experimental.session.list, backed by Session.listGlobal). When cwd is omitted it returns all known sessions; when cwd is supplied it filters by that directory. The existing live/in-memory ACP entries are still merged on top.

How did you verify your code works?

• bun typecheck in packages/opencode (and bun turbo typecheck --filter=opencode) — clean.
• bun test test/acp — 121 pass (updated the service-session mock to expose experimental.session.list).
• bun test test/server/session-list.test.ts test/server/global-session-list.test.ts — 14 pass.
• bun test test/cli/acp — 15 pass.
• prettier --check and oxlint on the changed files — clean.

Screenshots / recordings

N/A (logic change, no UI).

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 Found:

• PR fix(acp): list sessions across projects #33037 - fix(acp): list sessions across projects
  • fix(acp): list sessions across projects #33037

This PR appears to be directly related. Both PRs address the same issue of listing sessions across projects in the ACP. PR #33037 has a nearly identical title and appears to be working on the same problem. You should check whether #33037 is already merged or if it's the same fix being resubmitted.

[github-actions]

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