feat(cli): extend the OpenCode plugin to every documented context surface - #1487

Summary

OpenCode is the closest client to Claude-parity for models CBM has no first-party hook dialect for (DeepSeek, etc.): it already gets MCP + the skill + the three read-only agents, but its generated plugin only covered one of the four context surfaces other clients get through hook configuration. This PR extends cbm_client_adapter_opencode() so the generated cbm-augment.ts covers every surface OpenCode documents — and nothing it doesn't:

• grep/glob graph lookup (existing surface, improved): the plugin now pipes the event through hook-augment and unwraps hookSpecificOutput.additionalContext instead of pasting the raw Claude JSON envelope into the tool output.
• Post-read index-coverage notes: tool.execute.after for read maps OpenCode's filePath arg to the PostToolUse/Read event hook-augment already accepts.
• Session-start tier routing: OpenCode documents no context-output lifecycle hook, so the SessionStart note is carried on the first tool result of each session (deduped per sessionID).
• Post-compaction reinjection: via the documented experimental.session.compacting hook, appending to the mutable output.context array.

Every path stays fail-open (all failures resolve to ''; context is only ever appended), consistent with the hook-augment contract, and the plugin body remains marker-free so cbm_text_upsert_managed_block owns the lifecycle (regenerated on install/update, per the #616 lesson).

Why only these surfaces

Checked against the published OpenCode plugin docs: tool.execute.before/after, the event bus, and experimental.session.compacting are the documented context-capable hooks; there is no chat.message-style hook. Per CBM policy the generator does not invent undocumented vendor surfaces, so session-start context rides on the first tool result rather than a fabricated lifecycle hook.

Testing

• New test client_adapter_opencode_covers_lifecycle_read_and_compaction pins the four surfaces (SessionStart lifecycle, PostToolUse/Read with file_path mapping, compaction hook, additionalContext unwrap, per-session dedup).
• Existing client_adapter_opencode_sends_the_required_hook_event still passes unchanged (PreToolUse event, tool.execute.after, no registerTool, no markers in the body).
• agent_clients suite: 31/31 inside a full scripts/test.sh run; the emitted JS also validated standalone with node --check.
• Full-suite failures observed during verification were environmental (filed separately as Test suite assumes umask 022: activation-transaction fixtures fail on umask 002 machines #1483 and cbm_subprocess_spawn pays O(RLIMIT_NOFILE) close() calls per spawn (~0.8 s at nofile=524288) — use close_range() #1484) and reproduce on main without this change.

README's OpenCode matrix row updated to describe the four surfaces.

🤖 Generated with Claude Code