/create-adapter

name: create-adapter
description: >
  Create conversation adapters for importing AI chat history from different
  tools (Claude Code, Cursor, Warp, Codex, etc.). Covers the adapter.Adapter
  interface, caching strategies, incremental parsing, watch/FD management, and
  performance standards. Use when creating a new adapter, modifying adapter
  behavior, or debugging adapter performance issues. See references/ for
  Cursor DB and Warp SQLite schema details.

Create Adapter

Why Performance Matters

Adapters are the largest performance risk in Sidecar. Conversations refresh on watch events in a hot path that runs continuously during active sessions:

watch event -> coalescer -> session refresh -> adapter.Sessions() -> metadata parsing

If an adapter does full directory scans and full-file reparses on every change, CPU and FD usage spike quickly.

Reference Adapters

Study these before writing a new adapter:

• `internal/adapter/claudecode` - Incremental JSONL parsing, targeted refresh
• `internal/adapter/codex` - Directory cache, two-pass metadata parsing, global watch scope
• `internal/adapter/cursor` - SQLite/WAL-aware cache invalidation, FD-safe DB access
• `internal/adapter/pi` - Global scope, JSONL, CWD-based filtering, session classification, message prefix stripping

Required Interface

All adapters implement `adapter.Adapter`:

type Adapter interface {
    ID() string
    Name() string
    Icon() string
    Detect(projectRoot string) (bool, error)
    Capabilities() CapabilitySet
    Sessions(projectRoot string) ([]Session, error)
    Messages(sessionID string) ([]Message, error)
    Usage(sessionID string) (*UsageStats, error)
    Watch(projectRoot string) (<-chan Event, io.Closer, error)
}

Required Session Fields

Every session from `Sessions()` must set:

• `ID`, `Name`
• `AdapterID`, `AdapterName`, `AdapterIcon`
• `CreatedAt`, `UpdatedAt`
• `MessageCount`, `FileSize`

`FileSize` is used for dynamic debounce and huge-session auto-reload protection.

Treat source identity separately from lineage. Use the source's durable thread/session ID for `Session.ID`; parent, root, fork, or lineage IDs describe relationships and must not collapse distinct sessions. Decode metadata fields defensively when the source has emitted multiple shapes over time (for example, a string in one version and an object in another).

Path and Watch Strategy

Set `Session.Path` only when Sidecar should use tiered file watching for that adapter:

• **File-based append-only** (JSONL/log): set `Path` to absolute file path — this opts into TieredWatcher with HOT/COLD/FROZEN tiers
• **DB/WAL adapters** (Cursor, Warp, Kiro): prefer adapter-specific `Watch()` with WAL-aware invalidation; do not set `Path` unless tiered watching covers your write surface

**FROZEN tier**: File-based sessions with `Path` set automatically benefit from the FROZEN tier. Sessions unchanged for 24 hours (`FrozenThreshold`) are excluded from cold polling entirely — zero syscalls. They unfreeze when promoted to HOT (e.g., user selects the session). This is critical for adapters with thousands of session files; without it, `pollColdSessions()` does one `os.Stat()` per file every 30 seconds.

Performance Standards

1) Cache metadata and messages aggressively

Minimum cache keys:

• Metadata: `path + size + modTime`
• Messages: `path + size + modTime`
• SQLite/WAL: include WAL size+mtime in the key

Use bounded LRU behavior for every cache and index. Prune stale paths. Assume caches evict independently: a hit in one cache must restore any derived state required by another, or the authoritative source must remain available so eviction cannot change results such as aggregate usage or ID-to-path resolution.

2) Incremental parsing for append-only formats

For JSONL/event-log adapters:

• Cache last parsed byte offset
• Parse only appended bytes
• Fall back to full parse on shrink/rotation/corruption
• Preserve immutable head metadata from prior parse

3) Two-pass metadata for large files

When incremental metadata parse is impractical:

• Head pass: ID, CWD, first user message, first timestamp
• Tail pass: latest timestamp, token totals
• Skip middle of large files

When the source owns a metadata index, prefer its read-only index over scanning large event logs. Probe the schema and required columns before use, open it read-only with bounded/FD-safe access, and fall back to event-log discovery when it is missing, locked, or incompatible. The source index is an adapter seam, not a second source of truth to mutate.

4) Avoid repeated expensive path work

Resolve project path once per `Sessions()` call (`Abs`/`EvalSymlinks`), reuse for all matches.

5) Return defensive copies from caches

Never return cache-owned slices/maps directly. Copy message/session structures to avoid mutation bugs.

6) Keep DB access FD-safe

For SQLite adapters:

• Open read-only (`mode=ro`)
• `SetMaxOpenConns(1)`, `SetMaxIdleConns(0)`
• Close rows and DB handles promptly
• Avoid multiple DB connections per `Messages()` call

7) Preserve aggregate facts across incremental loads

Usage and similar cumulative facts may arrive as repeated totals or deltas. Define the source semantics, retain the authoritative aggregate across incremental parsing, and include all components the source exposes. Do not reconstruct a partial aggregate from whichever message cache entry survived eviction.

Watching and FD Management

1) Prefer directory-level watches

Do not watch per-session files when directory-level watch gives equivalent signals.

2) Implement watch scope

If adapter watches a global path (same location regardless of worktree):

func (a *Adapter) WatchScope() adapter.WatchScope {
    return adapter.WatchScopeGlobal
}

This prevents duplicate watchers across worktrees.

3) Always emit SessionID when known

Watch events should include session ID for targeted refresh (avoids full reloads).

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