Create Adapter

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).

4) Debounce and non-blocking sends

• Debounce bursty write events
• Use buffered channels
• Non-blocking sends: select { case ch <- evt: default: }

5) Leverage FROZEN tier for file-based adapters

File-based adapters that set Session.Path get TieredWatcher's three-tier system (HOT → COLD → FROZEN). Sessions unchanged for 24h are frozen and cost zero polling overhead. This is the primary defense against CPU spikes with thousands of session files. If your adapter has file-based sessions, always set Path — the FROZEN tier scales automatically.

6) Ensure cleanup

All watcher paths must close cleanly on plugin stop. No goroutine or FD leaks.

7) Combine known-file and discovery watching when needed

Tiered watching of known Session.Path values handles cheap appends, but it cannot discover a project's first session or a new time-partitioned directory. Global file adapters may need both known-file watching and one adapter-native discovery watcher. Watch creation at every directory level that can appear later (including month/year rollover), and keep discovery project-filtered.

8) Resolve path IDs through the adapter

Do not assume a new file's basename is its session ID. If identity lives in metadata, implement SessionPathResolver so watch events carry the same durable ID returned by Sessions().

Adapter Call Lifecycle

Some global adapters maintain caches and indexes across calls. Consumers must serialize calls to a stateful adapter, make gate admission and work lifecycle/epoch cancellable, and reject stale results after project switches or shutdown. A slow Sessions() result must remain observable and eventually load (with a visible loading state); never time it out, silently discard it, and leave its goroutine running. Global targeted refresh must admit only sessions already belonging to the current project; unknown IDs require a project-filtered discovery pass.

Message and Content Rendering

Adapters must provide rich structured content for Conversation Flow UI.

Required message mapping

Map source records to:

• Message.Role, Message.Content, Message.ContentBlocks
• Message.ToolUses (legacy compatibility)
• Message.ThinkingBlocks (if available)
• Message.Model when available

Tool linking rule

Use consistent ToolUseID for tool_use and tool_result blocks. If incremental parsing is used, preserve pending tool-link state across cache updates.

Optional Interfaces

TargetedRefresher

type TargetedRefresher interface {
    SessionByID(sessionID string) (*Session, error)
}

Reduces refresh from O(N sessions) to O(1). Implement when adapter can resolve a session directly.

ProjectDiscoverer

Implement when source format allows discovery of sessions beyond current git worktrees.

SessionPathResolver

Implement when a file path alone does not encode the source's durable session ID. Tiered and discovery watchers use it to turn new or changed paths into targeted refresh events.

ProjectDiscoveryWatcher

Implement for global sources that must discover the first matching session even when Sessions() initially returns no known files. Share only one global watcher per adapter, and ensure its events trigger a project-filtered load before any session is admitted.

Error Handling

• Detect(): return (false, nil) for missing data directories
• Sessions(): skip corrupt/unreadable entries and continue; hard-fail only on systemic errors
• Messages(): return nil, nil for missing session files; fail on parse errors
• Watch(): return (nil, nil, err) when watch setup fails
• Slow calls: surface loading/error state and accept the eventual result; do not translate a consumer timeout into a false empty history

Benchmark Targets

New adapters should meet these performance targets:

• Messages() full parse (~1MB): under 50ms
• Messages() incremental append: under 10ms
• Messages() cache hit: under 1ms
• Sessions() on 50 session files: under 50ms

Also benchmark realistic source shapes: hundreds or thousands of indexed sessions, a large live- scale transcript, cache hits, and incremental appends. Record fixture size and session/event count with the result so a tiny synthetic benchmark cannot hide discovery or parsing regressions.