# apps/server — BooChat backend (deep reference) — v2.7.x (last meaningful update: 2026-06)

> Per-app engineering notes for `apps/server/src/`. Cross-cutting commands, database, environment, workflow, and cross-app contracts (WS-frame / provider-type parity, sentinels) live in the **root `CLAUDE.md`**. This file auto-loads when you read/edit files under `apps/server/`.

## These gotchas are load-bearing — do not remove or refactor without understanding why
- Do NOT remove the abort-signal pinning comment in `stream-phase.ts` — `fullStream` exits cleanly on abort without throwing; the post-iteration `if (signal?.aborted)` check is the only thing that distinguishes cancelled from complete.
- Do NOT remove `includeUsage: true` from `provider.ts` — the adapter defaults it false; without it, token counts are always NULL.
- Do NOT add raw `broker.publish()`/`publishUser()` calls — always use `publishFrame`/`publishUserFrame` which Zod-validate against `WsFrameSchema`.

## Stack

- **Fastify** with `@fastify/websocket` and `@fastify/static` (serves the built frontend).
- **postgres** (porsager/postgres) with tagged-template SQL — no ORM. Schema in `schema.sql`, applied on startup. LSP may false-positive on `sql<Type[]>\`...\`` generics; CLI `tsc` / `pnpm build` is authoritative.
- **Zod** for request validation and config parsing.

## Key services

- **`services/inference/`** — Public surface re-exported via `inference/index.ts`; callers import from `./services/inference/index.js` explicitly (NodeNext doesn't honor directory-index resolution). Layout: `turn.ts` (runAssistantTurn/runInference/createInferenceRunner; exports `InferenceFrame`, `InferenceContext`, `TurnArgs`, `StreamResult`, `MAX_STEPS`); `stream-phase.ts` (streamCompletion AI SDK adapter + executeStreamPhase); `provider.ts` (`upstreamModel(baseURL, modelId)` wrapping `createOpenAICompatible` against llama-swap); `tool-phase.ts` (executeToolPhase → `ToolPhaseResult`; the turn loop lives in turn.ts, not recursion); `sentinel-summaries.ts` (cap-hit/doom-loop/step-cap summaries + inserters); `error-handler.ts` (handleAbortOrError, finalizeCompletion); `payload.ts` (buildMessagesPayload, loadContext, maybeFlagForCompaction, `OpenAiMessage`); `sentinels.ts` (`detectDoomLoop`, `DOOM_LOOP_THRESHOLD`); `budget.ts` (resolveToolBudget); `xml-parser.ts` (qwen3.6 XML tool-call fallback — KEEP, AI SDK doesn't handle inline-XML tool calls); `parts.ts` (`partsFromAssistantMessage`/`partsFromToolMessage`/`insertParts` — parts are the sole source of truth); `prune.ts` (two-tier compaction; `selectPruneTargets` is the pure helper); `types.ts` (`StreamPhaseState`, `DB_FLUSH_INTERVAL_MS`). **`TurnArgs`** is the per-turn state envelope, reset in `runInference` at the user-message boundary. Outer loop: `while (stepNumber < effectiveCap)`, `effectiveCap = Math.min(agent.steps ?? Infinity, MAX_STEPS=200)`. Per-agent `steps:` in AGENTS.md frontmatter; `steps: 0` = text-only. Step-cap hit writes a `cap_hit` sentinel (`CapHitSentinel.tsx` renders it).
- **AI SDK v6 streamCompletion adapter** (`services/inference/stream-phase.ts`). `streamText` is the underlying call; the BooCode layer (executeStreamPhase, finalize, dual-write) is shape-preserved via an adapter. Five gotchas the LSP/tests won't catch:
  - **Abort signals are swallowed.** `streamText`'s `fullStream` exits cleanly when `abortSignal` fires — no throw. Post-iteration `if (signal?.aborted) throw <AbortError>` is required, else the row finalizes `complete` instead of `cancelled`. Don't refactor away the pinning comment.
  - **Usage lands only at stream end** via `await result.usage` (v6 `inputTokens`/`outputTokens` → mapped to `promptTokens`/`completionTokens`). No mid-stream tok/s; ChatThroughput shows one value at stream end.
  - **Tools have NO `execute` field.** BooCode dispatches tools in tool-phase.ts, not the AI SDK loop — only `description` + `inputSchema: jsonSchema(parameters)`.
  - **`includeUsage: true` MUST be set on `createOpenAICompatible`** in `provider.ts`. The adapter defaults it false → no `stream_options.include_usage` → llama-swap emits no usage block → `result.usage` resolves `undefined` (NULL token counts). Don't remove during refactor.
  - **Tool-call-only turns may emit a leading `\n` text-delta.** `MessageList.flatten`'s `hasText` and `MessageBubble`'s `hasContent` both `.trim()` before the length check, else whitespace-only content renders an empty bubble + ActionRow between tool calls. `buildMessagesPayload` also skips `status='failed'` and complete-but-empty assistant rows (avoids "Cannot have 2 or more assistant messages at the end of the list" upstream rejection after cap-hit + Continue).
- **`services/inference/tool-shim.ts`** — Recovers structured tool calls from plain-text model output. Some models (notably Qwen) emit `<tool_call><name>...</name><arguments>...</arguments></tool_call>` inline text instead of structured JSON. `extractToolCalls(text)` parses both XML and JSON inline formats. `hasToolCallMarkup(text)` is a fast pre-check. Used as a fallback in the stream phase when structured `tool_calls` parse fails. Does NOT require `FAST_MODEL` — operates on the existing turn's output text.
- **`services/inference/loop-detectors.ts`** — Six detectors that catch repetitive model behavior: `detectContentRepeat` (same content N times), `detectToolLoop` (same tool called consecutively). `detectDoomLoop` combines both. These are additive to the existing `sentinels.ts` doom-loop detection.
- **AI SDK ModelMessage conversion** (`toModelMessages` in stream-phase.ts). Tool messages need a `toolName` for `ToolResultPart`; BooCode's OpenAI-shape history lacks it, so a forward-scan builds a `tool_call_id → toolName` map from prior assistant `tool_calls`. Tool outputs wrapped as `{ type: 'json' | 'text', value }` (v6 `ToolResultOutput`). Reasoning emits a `ReasoningPart` first in the content array.
- **`experimental_repairToolCall`** wired into `streamText` to keep the stream alive when qwen3.6 emits malformed tool args. Pass-through: logs the bad call, returns it unmodified; `executeToolPhase`'s zod-reject path routes it back to the model next turn.
- **`chat_status` frame** (via `broker.publishUser`) — `status: 'streaming' | 'tool_running' | 'waiting_for_input' | 'idle' | 'error'`. Frontend `useChatStatus` derives `idle_warm` (<30s since idle) vs `idle_cold`. `ChatThroughput` renders beside `StatusDot` only when streaming/tool_running, fed by 500ms-throttled `'usage'` frames (`completion_tokens` + `ctx_used` + `ctx_max`). `POST /api/chats/:id/discard_stale` marks a stuck-streaming row `failed` when the frontend's 60s no-token timer gives up.
- **Stale-streaming sweeps** (`apps/server/src/index.ts`): a boot-time pass after `applySchema()` and a periodic 60s `setInterval` both flip `messages.status='streaming'` older than 5 min to `failed` (publishing `chat_status='idle'`); the interval also runs `cleanupTruncations` (TTL + orphan reap of tmpfs truncation files). `onClose` hook clears the timer. Recovers from a container restart mid-stream.
- **`services/broker.ts`** — In-memory pub/sub, two channel types: per-session (message streaming) and per-user (sidebar). No persistence; clients reconnect on restart. Every WS publish goes through `broker.publishFrame(sessionId, frame)` / `publishUserFrame(user, frame)` — both Zod-validate against `WsFrameSchema` (`types/ws-frames.ts`) and fail-closed (log + drop). Schema single-sourced in `@boocode/contracts` (`packages/contracts/src/ws-frames.ts`); the package's `ws-frames.test.ts` enforces schema correctness. Don't add raw `broker.publish()`/`publishUser()` calls.
- **`services/tools.ts`** — Tool registry (`ALL_TOOLS`, `READ_ONLY_TOOL_NAMES`, `TOOLS_BY_NAME`). Filesystem tools (view_file/list_dir/grep/find_files) pass three guards: `path_guard.ts` (workspace scope), `secret_guard.ts` (filename deny list), `url_guard.ts` (SSRF/private-IP block for web_fetch). Web tools (`web_search`, `web_fetch`) are opt-in per chat via `session.web_search_enabled` (falls back to `project.default_web_search_enabled`) and filtered out of the LLM tool schema when false. Truncation: when a tool slice cuts content, `services/truncate.ts` stashes the full text on tmpfs (`BOOCODE_TRUNCATION_DIR`, default `/tmp/boocode-truncations`, 0o700) keyed by `tr_<12 base32>`; `view_truncated_output(id)` retrieves it. 5MB cap, 7-day TTL, reaped by the sweeper. Container restart loses retrieval — acceptable.
- **`services/compaction.ts`** + **`services/model-context.ts`** — Anchored rolling summary (single `summary=true` assistant row per chat, supersedes itself each compaction). Triggered when `chats.needs_compaction` is set after a turn exceeds `usable(ctx_max) = floor(0.85 × ctx_max)`. **`ctx_max` comes from `model-context.getModelContext()` fetching `${LLAMA_SWAP_URL}/upstream/<model>/props`** — NOT from `parsed.timings.n_ctx`. First inferences after boot may have `ctx_max=NULL` if llama-swap hasn't loaded the model; negative cache TTL 60s, recovers next turn. `buildHeadPayload` embeds `reasoning_parts` as a `<reasoning>...</reasoning>` prose prefix on assistant `content` (OpenAI wire shape has no structured reasoning field); standalone tag when content is empty. `buildHeadPayload` + `OpenAiMessage` exported for tests — keep them exported.
- **`services/system-prompt.ts`** — `buildSystemPrompt` is the string shim; `buildSystemPromptWithFingerprint` is the canonical impl returning `{prompt, fingerprint, drift}`. SHA-256 of the assembled prefix is logged per `buildMessagesPayload` (`prefix-fingerprint`, info); a `Map<sessionId, lastHash>` fires `prefix-drift` (warn) on change with a `changed_inputs` diff. The prefix is byte-stable in steady-state, so prefix caching is left to the input-layer mtime caches (BOOCHAT.md + AGENTS.md global/per-project in `agents.ts:safeStat`).
- **`services/inference/budget.ts`** — tool-call budgets: `BUDGET_READ_ONLY = 30`, `BUDGET_NON_READ_ONLY = 10` (forward-looking; no write tools yet), `BUDGET_NO_AGENT = 30` (every `ALL_TOOLS` tool is read-only today, so no-agent shares the read-only cap). Per-agent `max_tool_calls` from AGENTS.md overrides.
- **`messages_with_parts` view** (`schema.sql`). Read sites needing `tool_calls` / `tool_results` / `reasoning_parts` SELECT from this view, NOT `messages` — the legacy `messages.tool_calls`/`tool_results` JSON columns were dropped; the view reads parts-only subselects. Writes target `message_parts` via `insertParts` (or `partsFromAssistantMessage`/`partsFromToolMessage`). The `Message` wire type still carries `tool_calls?`/`tool_results?` because the view synthesizes them. Shapes: `tool_calls jsonb[]`, `tool_results jsonb` (single object), `reasoning_parts jsonb[]` of `{text}`. To UPDATE a message and return its full shape, do a two-step UPDATE returning `id` then SELECT from the view — RETURNING off bare `messages` no longer carries the tool fields. **`messages.model`** (attribution chip) stamps the model per assistant turn — at `finalizeCompletion` (BooChat + native coder) + the dispatcher's assistant-row INSERT (external coder); read via the view + the `message_complete` frame, rendered by `shortenModelName`.
- **`services/file_ops.ts`** — Shared file operation implementations used by both inference tools and HTTP routes.
- **`services/auto_name.ts`** — Non-streaming LLM call to generate 4-word session titles after the first assistant reply.
- **Provider picker dispatch**: when `provider !== 'boocode'`, the message route creates a `tasks` row (with `session_id` set) instead of calling `inference.enqueue`. The dispatcher (in `apps/coder`) picks it up and dispatches via ACP or PTY using the agent's `install_path`.

Route registration: all routes registered in `index.ts` via `register*Routes(app, sql, ...)`. Routes live in `routes/*.ts`.

## Server conventions

- **New tools** live in their own `services/<name>.ts` (see `web_search.ts`, `web_fetch.ts`) — a pure `executeFoo(input, ...deps)` for direct test access plus a `ToolDef` wrapper that `loadConfig()`s its real deps. Register the ToolDef in `tools.ts` `ALL_TOOLS` (and `READ_ONLY_TOOL_NAMES` if applicable). Inject `fetcher: typeof fetch = fetch` rather than `vi.spyOn(globalThis, 'fetch')`.
- **DB/session-aware tools** take an optional 4th `ToolExecCtx { sql, sessionId }` arg on `ToolDef.execute`, plumbed `executeToolPhase`→`executeToolCall`→`execute`. Optional so filesystem tools and the `apps/coder` `ALL_TOOLS` consumer stay compatible; filesystem tools ignore it. `read_tab_by_number` is the reference.
- **ReadableStream test stubs** use `pull()` (not `start()`) so chunks are produced lazily — `start()` enqueues everything and closes before the consumer reads, so a later `reader.cancel()` finds the stream closed and the `cancel()` callback never fires. Provide MORE chunks than the test consumes so the source stays 'readable' when cancel runs.
- Tool-name whitelists must derive from `ALL_TOOLS` in `services/tools.ts`, never hardcoded (this drift class hit `services/agents.ts` `ALL_TOOL_NAMES` before).
- Agent registry lives at `data/AGENTS.md` (global, bind-mounted at `/data/AGENTS.md`). No per-project `AGENTS.md` in this repo (removed to eliminate two-files-must-stay-in-sync drift); the `getAgentsForProject` per-project override mechanism remains for *other* projects.
- `data/AGENTS.md` is PARSED (`agents.ts` `splitSections`/`parseAgentSection`): each `## <Name>` is one agent and must be followed by a `---` frontmatter fence or the block throws; content before the first `## ` is discarded. Do NOT add free-form `## ` rule sections — they break the registry. Cross-cutting agent rules go in CLAUDE.md or a parser-ignored preamble.
- MCP stdio transport uses newline-delimited JSON (NDJSON), NOT LSP-style `Content-Length` headers. The boocontext MCP client (`services/mcp-client.ts`) is the reference (per the MCP spec, modelcontextprotocol.io/specification/server/transports).
- **`payload.ts:loadContext` SELECT** must include every `Session` field downstream code reads. The tool phase reads `session.allowed_read_paths`; if the SELECT omits it, cross-repo read grants silently fail. `sql<Session[]>` doesn't enforce column coverage, so the type doesn't catch it.
- **Secret guard safe patterns** (`services/secret_guard.ts`): `.env.example`, `.env.sample`, `.env.template`, `.env.defaults` are allowlisted via `SAFE_PATTERNS`. Do NOT add `.env.production`/`.env.development`/`.env.test` — those can hold real secrets.

