OpenCode compatibility: hook layer needs adaptation

[jsirish]

Context

throughline is tightly coupled to Claude Code's plugin hook system. The data layer (HANDOFF.md, logs, buffer) is already harness-agnostic via THROUGHLINE_DATA_DIR, but the hook layer needs adaptation for OpenCode.

Current State

Hook Architecture (Claude Code-specific)

hooks.json defines 5 Claude Code events:
- SessionStart → session-onboard.sh
- UserPromptSubmit → session-prompt.sh  
- PostToolUse → session-capture.sh
- PreCompact → session-precompact.sh
- SessionEnd → session-flush.sh

Claude Code Dependencies

• `` variable in all hook scripts
• Payload parsing assumes Claude Code's JSON structure:
  • .session_id (stable across compaction)
  • .tool_name, .tool_input, .tool_response
  • .source (startup/resume/clear/compact)
• Scripts use Claude Code's hook event names

What's Needed for OpenCode

1. Event Mapping

OpenCode needs to map its events to throughline's hooks:

OpenCode Event	throughline Hook	Notes
Session start	session-onboard.sh	Inject HANDOFF pointer + git state
User input	session-prompt.sh	Capture redacted prompts
Tool execution	session-capture.sh	Capture tool actions
Context compaction	session-precompact.sh	Stamp boundary marker
Session end	session-flush.sh	Safety-net stamp

2. Script Adaptations

• Replace `` with OpenCode's equivalent
• Adjust payload parsing for OpenCode's JSON structure
• Handle OpenCode's session ID mechanism (may differ from Claude Code's stable UUID)

3. Data Directory

THROUGHLINE_DATA_DIR is already portable - works across harnesses. Default .claude/throughline/ or custom path.

Implementation Options

Option A: Adapter Layer

Create an adapter that translates OpenCode events to Claude Code's format. Minimal changes to throughline scripts, but adds translation overhead.

Option B: Fork and Adapt

Fork throughline and adapt hook scripts for OpenCode's event system. More work upfront, but cleaner integration.

Option C: Abstract Hook Interface

Refactor throughline to define an abstract hook interface, with Claude Code and OpenCode as implementations. Most work, but enables multi-harness support.

Recommendation

Investigate OpenCode's hook/event system first to understand:

• What events are available?
• What's the payload structure?
• Is there a plugin system that can call shell scripts?

Then choose the implementation path based on OpenCode's capabilities.

Related

• README mentions cross-harness portability via THROUGHLINE_DATA_DIR
• Issue bug: a worktree's .claude/throughline/ is a frozen snapshot, not live-shared with the main tree #33 (worktree data sharing) is Claude Code-specific but the fix pattern could apply to OpenCode worktrees too