Add PromptEvent metric for tracking prompt events

[svarlamov]

Summary

Add PromptEvent metric (event ID 5) for tracking individual events within AI prompt sessions. Events are emitted as a side-effect of the existing checkpoint command — no separate command or hook configuration needed.

Event kinds

• HumanMessage — user prompts
• AiMessage — assistant text responses
• ThinkingMessage — assistant thinking blocks (Claude transcript only)
• ToolCall — non-file-editing tool invocations
• FileWrite — file-editing tool invocations (Edit, Write, etc.)

Design

• Single command: Prompt events emit from within the checkpoint handler, keeping hooks simple (one command per event)
• Content-based stable IDs: SHA256 of prompt_id:kind:content:index, prefixed with prompt_id
• Session state persistence: Tracks emitted events for idempotency and rollback detection
• Claude Code: Full transcript parsing with exact parent IDs
• All other agents: Generic handler using hook input data with estimated parent IDs

Agent support

All agents with hook mechanisms emit prompt events via their existing checkpoint hooks:

• Claude Code, Cursor, GitHub Copilot, Windsurf, Droid, Gemini, Amp, OpenCode

Key files

• src/commands/prompt_event.rs — core logic (transcript parsing, event emission, state management)
• src/commands/git_ai_handlers.rs — checkpoint handler calls emit_prompt_events_from_checkpoint
• src/metrics/events.rs — PromptEventValues metric definition
• agent-support/opencode/git-ai.ts — OpenCode plugin updated
• agent-support/amp/git-ai.ts — Amp plugin (prompt events via checkpoint)

Test plan

• 5 integration tests (transcript parsing, idempotency, rollback, growth, async_mode guard)
• 12 unit tests (event ID stability, state roundtrip, metric values, transcript parsing)
• All agent install_hooks tests pass (no duplicate hooks)
• cargo clippy clean, cargo fmt clean
• All Ubuntu CI checks passing

🤖 Generated with Claude Code

[devin-ai-integration]

Devin Review found 2 potential issues.

View 5 additional findings in Devin Review.

[devin-ai-integration]

🔴 truncate_for_hash panics on multi-byte UTF-8 characters due to byte-based slicing

truncate_for_hash uses s[..256] which indexes by bytes, not characters. In Rust, slicing a &str at a non-character-boundary panics at runtime. If user messages or AI responses contain multi-byte UTF-8 characters (emojis, non-ASCII text, etc.) and byte position 256 falls in the middle of a multi-byte character, this will panic and crash the process.

Codebase already handles this correctly elsewhere

Other files in the same codebase use safe approaches:

• src/commands/continue_session.rs:155-156: stdout.floor_char_boundary(MAX_DIFF_BYTES) with explicit comment "Use floor_char_boundary to avoid panicking on multi-byte UTF-8"
• src/commands/debug.rs:691: trimmed.chars().take(200).collect()
• src/commands/search.rs:591: text.chars().take(80).collect()

Suggested change

	if s.len() > 256 {
	s[..256].to_string()
	if s.len() > 256 {
	let safe_end = s.floor_char_boundary(256);
	s[..safe_end].to_string()

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[svarlamov]

Fixed in 9c8a087 — now uses s.floor_char_boundary(256) to avoid panicking on multi-byte UTF-8.

[devin-ai-integration]

Devin Review found 1 new potential issue.

View 10 additional findings in Devin Review.

[devin-ai-integration]

🟡 OpenCode file-edit tool events misclassified as ToolCall instead of FileWrite in prompt events

When process_generic_prompt_events processes hook data from OpenCode's file-edit tool checkpoints (PreToolUse/PostToolUse for edit, write, patch, multiedit), the tool_name is extracted at src/commands/prompt_event.rs:402-406 by looking for toolName in tool_input or tool_name at the top level. However, the OpenCode plugin's hook input for file-edit tools only includes filePath in tool_input (agent-support/opencode/git-ai.ts:92 and agent-support/opencode/git-ai.ts:138), never toolName. This causes tool_name to default to "unknown", and the event kind falls through to ToolCall instead of FileWrite at line 427. The new non-file-edit tool path at agent-support/opencode/git-ai.ts:111 correctly includes toolName, demonstrating the fix pattern — the file-edit hooks should also include toolName: input.tool in tool_input.

(Refers to lines 134-139)

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