feat(agent-adapter): probe and spawn opencode from the resolved binary (CODE-76)

[lucas77778]

Extracts the CODE-76 work from the code-248 branch as a standalone PR, rebased onto latest master (two cherry-picked commits).

Changes

• OpencodeProbe (src/probe/opencode.ts): detects a user-installed opencode CLI — daemon PATH scan plus the official install location ~/.opencode/bin, each candidate verified via --version (bare semver, anchored whole-output match). opencode joins ProbeableKind and the default prober set, so it now appears in the agent-runtime.list wire resource.
• opencode/serve.ts: all opencode serve spawns (per-session live server and the shared history server) now go through one owned spawn path — binary from agentRuntimeProber.resolveBinary('opencode') (managed → detected), bare-name PATH fallback for unprobed hosts. Replaces the SDK's createOpencodeServer, which hard-codes bare-name PATH resolution, cannot set cwd, and doesn't set windowsHide (Invariant 6).
• history-server.ts slims down to the manager logic, delegating spawn/readiness/termination to serve.ts.
• Docs and stale "opencode absent until CODE-76" markers updated across AGENTS.md, workbench hooks/onboarding, and the dev mock host.

Conflict resolution notes

The original commits were authored on the code-248 branch; cherry-picking onto master required resolving conflicts in AGENTS.md (root + agent-adapter) and history-server.ts imports. CODE-248 (pi adapter) context that leaked into the conflict hunks was deliberately excluded — this PR carries only the CODE-76 changes.

Verification

• pnpm check:ci — 0 errors
• pnpm test — 222 files / 1735 tests passed

[linear-code]

CODE-76

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[greptile-apps]

Greptile Summary

This PR adds probe-based OpenCode binary resolution and centralizes its server lifecycle. The main changes are:

• Detect OpenCode from PATH and its official install directory.
• Resolve managed or detected binaries before spawning.
• Share spawn, readiness, and shutdown logic across session and history servers.
• Report OpenCode through the agent-runtime resource.
• Update tests, mocks, and runtime documentation.

Confidence Score: 5/5

This looks safe to merge.

No blocking issues found in the changed code.

T-Rex Logs

What T-Rex did

• Validated the pre-run state showed the bare-name spawn failed even though the opencode binary existed.
• Validated the post-run state shows malformed version rejection, detection of server version 1.18.2, both server readiness paths, HTTP responses, and termination.
• Examined the invocation evidence showing both child processes executed the exact opencode binary with proper PATH, serve arguments, working directory behavior, inherited session CWD, config marker, and two SIGTERM exits.
• Assembled and uploaded runtime artifacts documenting the run, including the before-state, after-state, and invocation logs.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
packages/host/agent-adapter/src/native/opencode/serve.ts	Adds shared binary resolution, process spawning, readiness detection, and shutdown handling.
packages/host/agent-adapter/src/native/opencode/adapter.ts	Moves per-session OpenCode servers from the SDK spawn helper to the shared owned spawn path.
packages/host/agent-adapter/src/native/opencode/history-server.ts	Delegates history-server process mechanics while preserving neutral cwd, retries, and idle reaping.
packages/host/agent-adapter/src/probe/opencode.ts	Adds OpenCode executable discovery and bare-semver version validation.
packages/host/agent-adapter/src/probe/prober.ts	Registers OpenCode in the default runtime probe set.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  Probe[Probe OpenCode runtime] --> Managed{Managed binary?}
  Managed -->|Yes| Spawn[Spawn opencode serve]
  Managed -->|No| Detected{Detected binary?}
  Detected -->|Yes| Spawn
  Detected -->|No| Fallback[Bare PATH fallback]
  Fallback --> Spawn
  Spawn --> Session[Per-session server]
  Spawn --> History[Shared history server]
  Session --> Ready[Wait for listening URL]
  History --> Ready
  Ready --> Client[Create SDK client]
  Session --> Stop[SIGTERM then SIGKILL]
  History --> Reap[Idle reap]
  Reap --> Stop

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