# Reasonix Engineering Spec

> Reasonix is a coding agent: a thin harness driving multiple models, with **all
> capabilities supplied by configuration and plugins**. This document is the
> contract — code follows it. Change the contract first, then the code.

## 1. Design Principles

1. **Config- and plugin-driven core.** The core knows only interfaces. Concrete
   models and tools are resolved by name from registries, declared in config, or
   injected by plugins. No hardcoded `switch model`.
2. **Single static binary.** `CGO_ENABLED=0`; cross-compile with one command;
   CLI works out of the box.
3. **Lean dependencies.** Standard library by default. A third-party dependency
   must be pure-Go, lightweight, and must not compromise the single-binary /
   cross-platform / distribution story. TOML parsing is the one accepted dependency.
4. **Two extension tiers.** Compile-time built-ins (self-register via `init()`),
   and runtime external plugins (stdio JSON-RPC subprocesses, MCP-compatible).
5. **Interface-first & registry-based.** `Provider` and `Tool` are interfaces.
6. **Evolve, don't over-engineer.**

Language: **English is the primary language for all code** — comments,
user-facing strings, tool descriptions, system prompts, and this spec. The
README is bilingual (`README.md` English + `README.zh-CN.md`).

## 2. Layout

```
reasonix/
├── go.mod / go.sum          # module reasonix; require BurntSushi/toml
├── Makefile                 # build / cross / vet / fmt / test
├── README.md / README.zh-CN.md
├── reasonix.example.toml         # sample config
├── docs/SPEC.md             # this file
├── cmd/reasonix/main.go          # entry; blank-imports built-in providers/tools
├── cmd/reasonix-plugin-example/  # reference MCP stdio plugin (a runnable example)
└── internal/
    ├── cli/                 # subcommand routing, flags, assembly, exit codes
    ├── config/              # TOML loading (flag > project > user > defaults)
    ├── provider/            # Provider interface + types + kind→factory registry
    │   └── openai/          # OpenAI-compatible impl; init() registers "openai"
    ├── tool/                # Tool interface + Registry
    │   └── builtin/         # read_file/write_file/edit_file/move_file/bash/ls/glob/grep
    ├── permission/          # per-call Policy: allow/ask/deny rules → Decision
    ├── command/             # custom slash commands loaded from .reasonix/commands/*.md
    ├── plugin/              # stdio JSON-RPC (MCP) client; adapts remote tools
    ├── remote/              # SSH transport for the Remote-SSH module
    │   ├── forward/         # -L / -R port-forward lifecycle
    │   ├── sftpfs/          # SFTP file layer (quarantines pkg/sftp)
    │   └── bootstrap/       # detached `reasonix serve` bootstrap over SSH
    └── agent/               # Session + harness loop
```

Dependency direction (acyclic): `cli → {agent, plugin, config} → {tool, provider}`.
Built-in subpackages (`provider/openai`, `tool/builtin`) import their parent to
self-register; parents never import children. The Remote-SSH module layers
`cli → remote/bootstrap → remote → {remote/forward, remote/sftpfs, config,
netclient}`; `remote` and its subpackages never import `cli`, `agent`, or
`serve`, and all interactivity flows through callbacks (host-key / secret
prompts) so the desktop module consumes the same surface. See §Remote below.

## 3. Core Abstractions

### 3.1 Provider + registry (`internal/provider`)

```go
type Provider interface {
    Name() string
    Stream(ctx context.Context, req Request) (<-chan Chunk, error)
}

// Factory builds a Provider from a resolved config instance.
type Factory func(cfg Config) (Provider, error)

// Register adds a factory under a kind (e.g. "openai"). Called from init().
func Register(kind string, f Factory)

// New instantiates the provider of the given kind.
func New(kind string, cfg Config) (Provider, error)

type Config struct {
    Name    string         // instance name, e.g. "deepseek"
    BaseURL string
    Model   string
    APIKey  string
    Extra   map[string]any // kind-specific options
}
```

- The `openai` kind is an OpenAI-compatible `/chat/completions` implementation.
- **OpenAI-compatible vendors are config instances** of `kind = "openai"`,
  differing only in `base_url` / `model` / `api_key_env`. Adding another OpenAI-
  compatible model is a config edit, not a code change.
- **A provider is a vendor endpoint** (one `base_url` + `api_key_env`) that offers
  one or more models. `request_url`, when set, is the exact request target for
  OpenAI-compatible, Anthropic-compatible, and Responses providers. Legacy
  `chat_url` retains its historical OpenAI-only behavior; other legacy entries
  derive the protocol path from `base_url`. An entry declares either a single `model = "..."` or a
  `models = ["...", "..."]` list (with an optional `default`); the list form lets
  one vendor expose several models without re-declaring the endpoint/key. A
  **model reference** (`default_model`, the `--model` flag, the desktop switcher)
  resolves via `Config.ResolveModel`, which accepts a provider name (→ its default
  model), a bare model name, or an explicit `provider/model`. `context_window` is
  the provider-wide fallback; `model_overrides.<model>.context_window` can replace
  it for one model. Per-model `prices` use model IDs as keys.
- Streaming tool-call deltas are accumulated by index inside the provider; only
  complete `ToolCall`s are emitted.

### 3.2 Tool + registry (`internal/tool`)

```go
type Tool interface {
    Name() string
    Description() string
    Schema() json.RawMessage // JSON Schema for parameters
    Execute(ctx context.Context, args json.RawMessage) (string, error)
}
```

- Built-in tools self-register into a process-global builtin set via `init()`
  (`tool.RegisterBuiltin(t)`); `tool.Builtins()` lists them.
- A runtime `*Registry` is assembled per run: enabled built-ins (filtered by
  config) **plus** plugin-provided tools. The agent only sees the `*Registry`.
- Tool schemas are canonicalized on registry insertion. The built-in contract is
  documented in [`TOOL_CONTRACT.md`](TOOL_CONTRACT.md) and backed by tests that
  compare the documented surface against the same canonical schema path.
- `Execute` parses raw JSON args itself. Errors are returned, not fatal — the
  agent feeds them back so the model can self-correct.

### 3.3 Plugins (`internal/plugin`) — MCP client

An external plugin is an MCP server declared in config. The wire protocol is
**JSON-RPC 2.0** in every case; only the transport differs. A `transport`
interface (`call` / `notify` / `close`) abstracts that, so the MCP-level logic
(handshake, `tools/list`, `tools/call`, …) is written once.

- **Transports** (config `type`):
  - `stdio` (default) — a local subprocess; one JSON message per line over the
    child's stdin/stdout (the MCP stdio convention). Declared with
    `command` / `args` / `env`; terminated on ctx cancel / shutdown.
  - `http` (a.k.a. `streamable-http`) — a remote server at `url`. Each request
    is an HTTP POST; the server replies with either `application/json` (one
    response) or `text/event-stream` (an SSE stream carrying the response plus
    any server notifications). The `Mcp-Session-Id` response header, once seen,
    is echoed on subsequent requests. Static `headers` (e.g. a bearer token) are
    sent on every request. When no static `Authorization` header is configured,
    user-initiated OAuth uses Protected Resource Metadata and Authorization
    Server Metadata discovery, dynamic client registration, PKCE S256, a
    loopback callback, resource indicators, and refresh-token rotation. Client
    credentials and tokens are stored with mode `0600` in the server's private
    Reasonix MCP state directory, outside the workspace; tokens are bound to the
    configured resource URL and are never reused after that URL changes. OAuth
    discovery, registration, and token requests honor Reasonix's resolved
    network-proxy settings. Removing a declaration clears this state unless the
    effective fallback uses the same OAuth resource.
  - `sse` — the legacy 2024-11-05 HTTP+SSE transport. A persistent GET stream
    receives an announced relative POST endpoint, JSON-RPC responses, and server
    messages. Cross-origin announced endpoints are rejected so static headers
    cannot leak.
- `${VAR}` / `${VAR:-default}` are expanded in `command`, `args`, `env`, `url`,
  and `headers` so secrets come from the environment, not the config file.
- Lifecycle: `initialize` → `notifications/initialized` → `tools/list`;
  invocation via `tools/call {name, arguments}`.
- When a workspace root exists, initialize advertises `roots` and transports
  answer `roots/list` with its file URI. `tools/call` includes a per-call
  `_meta.progressToken`; matching `notifications/progress` messages stream into
  the existing tool-progress event path.
- A stdio server uses one persistent transport for initialize, reads, and
  writes, preserving state such as browser sessions across tool calls. The
  process uses the server's process sandbox because process confinement cannot
  change per RPC; read-only eligibility and destructive filtering remain local
  workflow gates rather than separate process sandboxes.
- Configuration provenance is runtime metadata and determines persistence scope.
  Desktop and CLI installs write the user-global `config.toml`; project
  `reasonix.toml` and `.mcp.json` entries remain in their owning project file.
  Every configured source is trusted without a separate launch-confirmation
  step. Project entries override same-name global entries, and project
  `reasonix.toml` overrides `.mcp.json`. Editing writes to the effective entry's
  source; removing it reveals the next lower-priority declaration.
- Each remote tool is adapted to the `Tool` interface and injected into the run
  registry, namespaced `mcp__<server>__<tool>` (spaces normalised to `_`) to
  match Claude Code and avoid clashes.
- A tool's MCP `annotations.readOnlyHint` maps to `Tool.ReadOnly()`. It defaults
  to false (a remote tool is opaque — we can't see its side effects), so a
  plugin opts a tool into parallel-batch dispatch and the permission layer's
  reader-default by declaring `readOnlyHint: true` in `tools/list`.
- Installation is the trust decision for tool metadata. Reasonix assumes an
  installed server reports `readOnlyHint` and `destructiveHint` honestly;
  planner/read-only filtering is a workflow boundary for trusted servers, not
  containment against a malicious MCP server. Explicit deny rules and the
  process sandbox remain host-controlled boundaries.
- `prompts/list` + `prompts/get` surface as `/mcp__<server>__<prompt>` slash
  commands; `resources/list` + `resources/read` are referenced as
  `@<server>:<uri>` in chat. `/mcp` shows connected servers and their counts.
- `cmd/reasonix-plugin-example` is a runnable reference stdio server (`echo`,
  `wordcount`), driven by an end-to-end test that builds the real binary.

### 3.4 Agent (`internal/agent`)

- `Session` holds `[]Message`.
- `Run(ctx, input)` loop: build `Request` (with tool schemas) → `provider.Stream`
  → print text deltas live, collect complete tool calls → if none, done; else
  execute each tool (built-in or plugin) and append results → repeat, bounded by
  `maxSteps`. `ctx` threads throughout (Ctrl-C aborts in-flight requests).
- A `Runner` is anything with `Run(ctx, input) error`; both `Agent` and
  `Coordinator` satisfy it, so the CLI is agnostic to single- vs two-model mode.

### 3.5 Two-model collaboration (`Coordinator`)

When `agent.planner_model` names a provider different from the executor, a
`Coordinator` runs two models in **separate sessions** to keep each one's prompt
prefix cache-stable:

- The **planner** (low-frequency) runs in its own session with the same standing
  memory context plus a filtered read-only research tool set, then produces a
  concise plan. A deterministic host policy defaults to executor-only. It
  invokes the dedicated planner only for an explicit plan-first /
  plan-then-execute request, an explicit wait-for-approval boundary, an
  explicit plan-only request, or an explicit Goal start. It does not call a
  classifier model, does not infer complexity from wording, file count, or
  keywords, and does not infer host state from controller-authored prompt
  blocks. Explicit Plan Mode is an executor-driven workflow and never starts a
  second planner. Synthetic turns, short contextual replies, and ordinary
  requests stay executor-only. There is no Light/Full planning depth. The
  privacy-safe route/reason decision is emitted in phase detail.
- The planner uses one stable system prompt. Only a small host-authored
  `<planner-turn>` block names the explicit route. The plan distinguishes
  verified from candidate touchpoints and records non-goals, risks, acceptance
  criteria, and command-level verification when the evidence supports them. If
  the planner still does not finalize after the bounded research and grace
  round, plan-and-execute falls back to the executor with the pristine task;
  plan-only and plan-for-approval remain fail-closed. The incomplete planner
  turn is rolled back rather than exposed as a broken manual continuation.
- A bare plan-first route hands the completed plan directly to the executor.
  Plan-for-approval is reserved for an explicit request to wait for
  confirmation; the host enforces that boundary even if the planner omits its
  marker, then hands the approved plan to the executor. A headless host persists
  the plan so a later turn can continue. Explicit plan-only requests persist the
  plan and end the current turn without execution. A planner failure on either
  execution boundary cannot fall back to the executor. These directives may
  appear after the task clause; quoted examples do not change the route.
- The plan is handed off as structured text to the **executor** — a full
  tool-using `Agent` in its own session — which validates candidate assumptions
  and carries it out.
- The sessions never mix, so neither model's prefix is disturbed by the other's
  turns; both grow prepend-only and stay cache-friendly. This reconciles
  "cache-first" with "two-model collaboration": switching models *inside one
  shared conversation* would break the prefix and tank cache hits, so we don't.

### 3.6 Context management (content-driven summary)

Long tasks fill the model window. Reasonix keeps a **cache-first, append-only**
canonical transcript and installs a short **provider-visible checkpoint** only
when the sole automatic threshold is crossed.

- Each provider declares `context_window` (tokens). The only automatic trigger is
  `agent.compact_ratio` (default **0.80**; presets 0.70 / 0.80 / 0.85; range
  0.65–0.85).
  `triggerTokens = floor(context_window × compact_ratio)`.
- **Below the trigger** ordinary requests remain append-only and no sidecar is
  written. Every provider request uses the durable, bounded tool `Content`;
  local `RawContent` is never promoted into sampling, retry, summary, or replay.
- **At the trigger** one singleflight maintenance transaction first persistently
  prunes every tool result over 8192 Unicode code points to `4096 head +
  "[... tool result middle pruned ...]" + 1024 tail`. If this clears pressure,
  no summary request is made. Otherwise Reasonix summarizes the old contiguous
  prefix and retains the newest **16%** of the context window verbatim, aligned so
  assistant tool calls and tool results are never split.
- The summary request replays the original system message, the selected message
  prefix, and the ordinary request's tool schemas, then appends one final user
  compaction instruction. This shape can reuse provider KV cache. Output is capped
  at **8192 tokens**. A pressure run may make one additional convergence summary
  (at most two successful summaries total); overflow makes at most one summary and
  retries the original request at most once after projection-version progress.
- A checkpoint must be strictly smaller than the replaced full request. Summary
  timeout/error/empty/max-token results never produce a mechanical digest. Below
  the hard ceiling the latest durable projection continues; at overflow or the
  hard ceiling an insufficient prune returns `ErrCompactionRequired`.
- Users inspect or change the threshold with
  `reasonix config compact-ratio [--local] [VALUE]`. Project config overrides the
  user-global value used by desktop and new CLI sessions. UI always shows the
  **effective** ratio.
- `max_output_tokens` is an independent **per-turn** completion ceiling and
  never changes `triggerTokens` / `compact_ratio`.
  - `0` is the provider auto value. Local admission uses the provider
    capability (official DeepSeek 384K, OpenCode Go model table, or a learned
    completion budget). It is **not** “skip the local output check”.
  - Official DeepSeek Chat/Responses still omit the field when the remaining
    shared window can host the 384K auto budget, and inject a clipped value
    only when the window is tight. Official DeepSeek Anthropic always sends
    384K or the clipped remainder because `max_tokens` is required.
  - Official OpenCode Go presets send `min(model max, physical remaining)` on
    the generic `max_tokens` / `max_output_tokens` field. Third-party
    compatible APIs do not assume a shared window until a trusted context 400.
  - A positive value is an explicit cost cap and may still be clipped down to
    the physical remainder. A negative value force-omits optional wire limits;
    if the known auto budget no longer fits, Reasonix compacts instead of
    overriding that choice.
- Canonical tool storage remains backward compatible: `Content` is the stable
  provider-visible ≤32KB form and `RawContent` holds the full local original.
  Full results are returned to the model only after an explicit paged
  `use_capability` call to `session:tool_result`; sampling, stream retry, summary,
  and projection replay all use the same bounded `Content`. Prune projections
  never rewrite either canonical field. Older supported readers remain bounded.
- Automatic maintenance is planned once in `ContextManager.Prepare` from the
  current projection plus the append-only canonical tail. The canonical
  transcript is never rewritten. Subsequent thresholds merge
  **prior digest + new history** into a single digest (no multi-span merge, no
  application-layer retry). Failure records a generation-scoped
  `blocked`/`failed` receipt; the same generation does not pay for another
  automatic summary. Manual `compress` can retry.
- Old multi-threshold keys (`soft_compact_ratio`, `tool_result_snip_ratio`,
  `compact_force_ratio`, `cold_resume_prune`, `context_editing`) are removed on
  ordinary start and ignored at runtime. Native provider tool clearing is not
  used; every provider uses the local summary checkpoint path.
- `keep` / `recent_keep` remain readable and round-trip for compatibility but are
  deprecated and ignored by compaction. Old user turns, failed tool results, and
  `[[keep]]` messages enter the summary prefix. Restart restores an existing
  checkpoint without re-summarizing or replaying timeline cards.
- Full history remains in the session transcript. The read-only `history` tool
  provides BM25 retrieval over sessions; new summary checkpoints do not create
  prune archives.
- The read-only `history` tool gives the agent on-demand BM25 retrieval over
  saved session JSONL files. `scope="project"` searches the current controller's
  session directory; `scope="global"` also searches the user-global session
  directory and compacted-history archives. `operation="around"` can then read a
  bounded transcript window around a returned hit. Search keeps the best hit and
  trims trailing common-word-only noise with a relative score floor; a 0-result
  response tells the agent how to retry with rarer terms or widen scope.
- The read-only `memory` tool gives the agent on-demand search/list/read access
  to saved auto-memory files. It complements the writer tools: `memory` checks
  what already exists, `remember` saves or updates a fact, and `forget` removes
  a stale one from the active index while archiving the file for traceability.
  Archived memory files are visible in local management surfaces (`/memory`,
  TUI, desktop panel) but are excluded from active-memory retrieval. Memory
  search uses the same relative BM25 floor and guides the agent to fall back to
  history when exact original wording or tool output matters.
- Before each real user turn, bounded BM25 recall selects relevant active facts
  from the raw user message and appends them as a low-authority user-turn suffix.
  Generic turns are suppressed, project facts override equivalent global
  fallbacks, stale facts are down-ranked, and recall is bounded by result/character
  budgets. This never mutates the stable system prompt or tool schemas.
- The owning controller may auto-allow only a bounded, non-sensitive,
  create-only project/reference `remember`, including in a top-level headless
  run. In Ask, global facts, preferences, feedback, updates, duplicates,
  sensitive/oversized content, and every `forget` require a fresh human
  approval. Interactive Auto treats `remember` and `forget` as normal policy
  fallback while preserving explicit `ask` and `deny` rules. Interactive YOLO
  bypasses memory ask prompts unless an explicit deny rule matches.
  Guardian/safety review cannot answer these prompts on the user's
  behalf. Sub-agents and headless surfaces without the owning scoped
  controller fail closed, including headless YOLO except for the create-only
  path above. The approval request includes a compact preview, while
  external notification hooks only receive the tool name.
- Facts carry immutable IDs, monotonic revisions, timestamps, type, and scope.
  Updates snapshot the previous revision; restore and archive recovery create a
  higher revision and reject path escapes, symlinks, collisions, and overwrites.
  User-initiated memory edits in the local UI are already explicit user actions.
  See [`SESSION_MEMORY_RETRIEVAL.md`](SESSION_MEMORY_RETRIEVAL.md) for the
  detailed implementation contract.

**What survives a fold.** The system prompt and newest 16% tail survive verbatim.
Every older model-visible message forms one contiguous summary prefix, including
user turns, failed tool results, prior digests, and `[[keep]]` messages. Exact
older wording remains available in the canonical transcript and through the
read-only `history` tool. `keep` and `recent_keep` are compatibility-only fields.

Subsequent folds merge the current digest with newer old history into one digest.
Compaction only writes a projection: canonical storage keeps every original, so
a missed detail stays recoverable through `history`.

Prune and summary commits are deliberate cache-reset points. Between maintenance
runs the session remains append-only and cache-friendly. `context_window = 0`
disables automatic compaction for an instance.

### 3.7 Permissions (`internal/permission`) — per-call gating

A coding agent runs shell commands and edits files autonomously. The permission
layer decides, **per tool call**, whether to allow it, deny it, or ask the user
first. It is independent of the model and of the CLI — the agent consults a
`Gate` interface at execute time; the gate is built from a static `Policy` plus
an optional interactive `Approver`.

```go
type Decision int            // permission package
const (Allow Decision = iota; Ask; Deny)

// Policy evaluates static rules against a tool call. Pure, no I/O.
type Policy struct { Mode Decision; Allow, Ask, Deny []Rule }
func (p Policy) Decide(toolName string, readOnly bool, args json.RawMessage) Decision
```

- **Rule syntax.** A rule is `Tool` (matches any call in that tool family) or
  `Tool(specifier)` (matches when the call's *subject* matches the specifier).
  Bash and file mutation approvals use Claude Code-style families such as
  `Bash(npm run build)`, `Bash(npm run test:*)`, and `Edit(docs/**)`. Built-in
  file mutations include writes, edits, notebook edits, symbol/range deletes,
  and `move_file` renames/moves. Legacy lowercase tool IDs still load for
  compatibility. `Bash=<literal>` is the exact-command form: metacharacters in
  the literal are ordinary characters and only the identical complete command
  matches. The
  `:*` suffix marks a Bash command-prefix approval; generated prefix rules also
  reject later commands that introduce shell operators, so `Bash(go test:*)`
  does not cover `go test ./... && rm -rf tmp`.
  Legacy `Bash(go test *)` prefix rules still load, but new rules are saved as
  `Bash(go test:*)`. The subject is extracted generically from the call's JSON
  args by a small set of
  known keys — `command` (bash), `path` / `file_path` (file tools), `pattern`
  (grep/glob) — so tools need not change. A rule whose subject the args don't
  expose only matches in its bare `Tool` form.
- **Dynamic Bash.** Parameter/arithmetic expansions, assignments, heredocs, unproved
  redirects, and shell globs cannot reuse bare Bash, prefix, or glob allows;
  remembered approvals are exact `Bash=<literal>` rules. They still follow the
  normal posture fallback, so Auto and an approved-plan window may execute them
  without prompting. Nested or indirect execution is stricter: command and
  process substitution, a dynamic command name, parse failures, `eval`,
  `source`, shell `-c`, PowerShell/cmd command strings, and runtime inline-code
  flags require a human in interactive Ask/Auto. Guardian, allowing hooks, and
  the approved-plan window cannot answer that decision; only an identical exact
  grant or YOLO can bypass it by default. The advanced
  `[permissions] allow_dynamic_bash = true` opt-in lets an Allow fallback,
  including Auto, cover this class; explicit `ask` and `deny` rules retain
  precedence.
- **Precedence.** `deny` > `ask` > `allow` > fallback. Fallback is `Allow` for
  read-only tools and `Mode` (default `Ask`) for writers. `deny` always wins, so
  a broad `allow = ["Bash"]` can still be carved by `deny = ["Bash(rm -rf*)"]`;
  conversely `ask` overrides a broad `allow` to force a prompt on a risky subset.
- **Resolving `Ask`.** The interactive front-end (the chat TUI) prompts the user
  — allow once / allow this approval scope for the session / always allow this
  approval scope / deny — via an `Approver`. For Bash, the default scope is the
  concrete command subject, and the user may choose a conservative command-prefix
  scope when available (for example `Bash(go test:*)`) so similar invocations in
  the same session or saved config do not prompt again. For file-mutation tools,
  a session grant covers editing for the rest of the session while a persisted
  grant is path-scoped when a path is available, stored as `Edit(<path>)` so all
  built-in file-mutating tools share it. A
  non-interactive run
  (`reasonix run`, a sub-agent, anything with no TTY / no approver) cannot prompt.
  Its explicit posture therefore resolves without blocking: Ask/manual fails
  closed, Auto allows only ordinary writer fallback, and YOLO may bypass ordinary
  Ask decisions. Nested or indirect Bash remains stricter: headless
  Ask/Auto/DontAsk reject it unless an identical literal grant exists; YOLO or
  `allow_dynamic_bash = true` with an Allow fallback may opt out. A `Deny` is a
  hard block in *every* mode: the tool never executes and the model receives a
  "blocked" result it can adapt to (the same shape as a plan-mode refusal).
- **MCP authorization.** Installing an MCP server authorizes all of its tools;
  there is no second server, raw-tool, writer, or destructive approval policy.
  Project configuration is trusted the same way and requires no separate launch
  confirmation. Explicit global deny rules still win. `readOnlyHint` and
  `destructiveHint` remain internal
  facts for scheduling, Plan/read-only restrictions, and cached-to-live safety
  reclassification. Strict read-only sub-agent registries expose only
  authorized tools with `readOnlyHint: true` and no `destructiveHint`. The
  two-model Planner uses the fixed `use_capability` proxy (never direct
  `mcp__*` schemas) for authorized, non-destructive MCP without requiring
  `readOnlyHint`; destructive tools are left for the Executor. In Balanced
  two-model sessions the Executor owns an isolated frontend for the same proxy,
  so Planner-discovered capability IDs remain executable after handoff. Schema-only
  changes refresh the next-session cache without adding an execution approval
  or retry. Immediately before dispatch, the proxy re-checks the current
  controller's enablement, authorization, and complete runtime connection
  identity; a same-name client on a shared Host is never sufficient authority.
- **Relationship to plan mode.** Plan mode (§3.4) is a plan-first collaboration
  workflow, not an all-tools read-only mode. Before Permissions/Sandbox, the
  host enforces explicit phase opt-outs (`complete_step` is read-only but
  belongs to the post-approval execution phase, so it self-reports plan-unsafe
  and is refused). The dedicated two-model Planner may call authorized,
  non-destructive MCP even when `readOnlyHint` is absent; it hard-blocks
  destructive targets and readers from unauthorized servers for the entire
  planning phase. A single-model Plan without the dedicated Planner continues
  to block MCP writer/destructive targets while Plan is active.
  Ordinary built-in and Bash calls then use the same Ask/Auto/YOLO, explicit
  `ask`/`deny`, and Sandbox path as Standard mode. A third-party MCP
  `readOnlyHint` affects dispatch classification and strict-child eligibility,
  but not the dedicated Planner's non-destructive trust path. Once the server is
  installed or declared in project configuration, all non-destructive
  capabilities enter the dedicated Planner proxy; only hinted readers enter
  strict read-only sub-agent execution. `plan_mode_read_only_commands` is
  retained for config/session round trips and does not grant or revoke calls in
  the main Plan workflow. `read_only_task` and `read_only_skill` remain strict
  read-only capabilities with their own tool registry and safe foreground Bash;
  writer-capable `task` and skill execution remain permission-gated instead of
  Plan-blocked, and their child turns inherit the Plan workflow marker and
  explicit phase opt-outs.
- **User decisions are separate from tool approvals.** Runtime tool approval has
  three user-facing postures: `ask` ("需要批准"), `auto` ("自动批准"), and
  `yolo` ("Yolo批准"). `auto` lets the permission policy auto-approve the writer
  and interactive memory fallback while preserving explicit ask/deny rules;
  `yolo` skips ordinary tool permission prompts for approval-gated tools such
  as writers, Bash, and explicit interactive `remember`/`forget` ask prompts.
  Explicit deny rules and forced fresh reviews
  for plans, sandbox escapes, and managed config writes still apply. Nested or indirect Bash
  commands require a human in interactive Ask/Auto even during the approved-plan
  window; ordinary expansions, assignments, redirects, and globs continue under
  Auto fallback but cannot inherit reusable Bash rules. YOLO is the sole mode
  bypass for the human-required class, while an identical exact literal remains
  an ordinary explicit authorization.
  Neither posture answers `ask` questions or approves `exit_plan_mode` plans.
  Plan Mode is entered only through an explicit user choice and remains
  independent of the active tool-approval posture. After a user approves a
  plan, the controller opens a short `approvedPlanAutoApproveTools` execution
  window so the model can perform the approved writes without re-prompting; that
  transient window still does not auto-approve future plans. In headless `ask`
  execution, any fallback answer is labelled as a model assumption, not as a
  user decision.

- **Collaboration mode is separate from tool approval.** The desktop composer
  presents collaboration as `normal` ("正常模式"), `plan` ("计划模式"), and
  `goal` ("目标模式"). `/goal <objective>` starts an autonomous, session-scoped
  active goal: the controller prepends goal context to user turns outside the
  cache-stable system prompt and keeps issuing continuation turns until the
  model reports completion, repeats the same blocked state three times, the user
  stops it, or the safety continuation limit is reached. Blocked-state matching
  is normalized for casing, whitespace, and punctuation so minor wording drift
  does not reset the audit; restarting a goal begins a fresh blocked audit. A
  goal is treated as a task contract: if the objective includes Context,
  Request, Output format, Constraints, or Pause policy sections, those sections
  define the autonomous work boundary. When they are absent, the model infers a
  lightweight contract from the conversation and workspace. The injected goal
  block tells the model to pause only for irreversible or externally visible
  operations, scope changes, or information only the user can provide; ordinary
  uncertainty should be handled with sensible defaults and reported as an
  assumption. Completion requires the concrete request, output format,
  constraints, and relevant verification expectations to be satisfied or
  explicitly reported as unverified.
  Goal has no default model-round, cross-Run turn, wall-clock, or numeric
  no-progress boundary. Goal-scoped novelty accepts new read/search results and state changes
  but rejects exact tool/argument/result repeats. All classes use the same Goal
  FSM, host receipts, Delivery readiness, and bounded evaluator; there is no second research
  protocol or writable sidecar runtime. Legacy `.reasonix/autoresearch/...`
  archives remain read-only and explicit old paths recover as ordinary Goals.
  Outside goal mode, ordinary prompts never change collaboration mode; the user
  must choose Goal or use `/goal` explicitly.
  Repeated host failures, zero-evidence rounds, and Todo stalls trigger bounded
  strategy redirects and intervention-epoch resets, never a Goal pause. Turns,
  tokens, provider requests, and active work duration remain observational when
  the corresponding budget is not configured. Positive user-selected
  `[agent].goal_token_budget`, `max_steps`, time, and cost budgets remain
  explicit resumable boundaries. The Goal token budget defaults to `0` (off);
  resuming a `budget_spend` pause grants a fresh slice without clearing
  cumulative Goal statistics. `task_time_budget_minutes = 0` (and legacy
  negative values) disables the time boundary.
  `/goal clear` removes the active goal. Switching into plan/normal mode clears
  the active goal in the desktop UI so the collaboration mode remains one of
  the three choices, while the underlying tool approval posture is preserved.

| Tool approval posture | Tool approvals | Plan approval | `ask` questions |
| --- | --- | --- | --- |
| Need approval / `ask` | Follow permission policy (`Ask` prompts interactively) | Waits for user | Waits for user |
| Auto approve / `auto` | Writer fallback and interactive `remember`/`forget` fallback auto-allowed; explicit ask/deny rules still apply | Waits for user | Waits for user |
| YOLO approval / `yolo` | Ordinary prompts auto-allowed, including `remember`/`forget`; deny rules and plan/sandbox/config reviews remain | Waits for user | Waits for user |
| Approved-plan execution window | Approved plan's writer fallback is auto-allowed; explicit `ask` / `deny` rules remain | Future plans still wait | Waits for user |

Out of the box (`mode = "ask"`, no rules), interactive `reasonix` prompts before
each writer/bash call and `reasonix run` fails closed on those calls because it
has no approver. Use `reasonix run --auto ...` / `-y` to allow ordinary writer
fallback in unattended automation; `--permission-mode auto` is equivalent.
Explicit `ask` rules still fail closed under Auto, and `deny` rules harden every
posture.

### 3.8 Slash commands (`internal/command`)

The chat TUI accepts `/command` input. Three kinds share one dispatch:

- **Built-in actions** (`/compact`, `/new`, `/clear`, `/effort`, `/mcp`, `/help`) manipulate session
  state locally and never reach the model. `/new` starts a new session while
  saving the previous transcript for resume/history. `/clear` requires
  confirmation, then discards the current context without saving it; it does not
  delete project memory.
- **Custom commands** are Markdown files under `.reasonix/commands/` (project) and
  the user config dir, e.g. `~/.reasonix/commands/` on macOS/Linux; the project dir overrides the user dir on a
  name clash. A file `review.md` becomes `/review`; a subdirectory namespaces it
  (`git/commit.md` → `/git:commit`). Invoking one renders its body and sends the
  result as the next user turn.
- **MCP prompts** (§3.3) appear as `/mcp__<server>__<prompt>`.

```markdown
---
description: Review the staged diff
argument-hint: [focus-area]
---
Review the staged diff. Focus on $ARGUMENTS, list bugs with file:line.
```

- Frontmatter is an optional `---`-fenced block of simple `key: value` lines;
  `description` and `argument-hint` are recognised (no YAML dependency — Reasonix
  stays lean). The remainder is the body template.
- Substitution in the body: `$ARGUMENTS` (all args, space-joined), `$1`…`$N`
  (positional, empty when absent), `$$` (a literal `$`). Arguments are the
  space-separated tokens after the command.
- Loading is pure (`command.Load(dirs...)`) and tested; a malformed file is
  skipped, not fatal. Custom and MCP-prompt commands both resolve to text and
  reuse the same "start a turn" path as a typed message.

#### CLI modal/composer ownership

The Bubble Tea chat TUI has one bottom composer. A slash-command overlay must
declare whether it owns keyboard input:

- **Modal overlays** own navigation/confirm/cancel keys and must hide the
  composer while open. Examples: `/mcp`, `/resume`, `/rewind`, approval prompts,
  and non-typing `ask` choice cards.
- **Input-owned overlays** are attached to the textarea and must keep the
  composer visible. Examples: slash/@ autocomplete and `ask` free-text mode.

New CLI overlays must update `chat_tui.hideComposer()` and add/extend layout
tests so `bottomRows()` accounts for either `panel + status` or
`panel + composer + status`. This prevents inactive chat input boxes from being
rendered under modal panels.

### 3.9 Chat references (`@`)

A chat message may embed `@` references; before the turn is sent, each is
resolved and prepended to the message as a tagged block the model can read.

- `@<server>:<uri>` where `<server>` is a connected MCP server → an MCP
  resource (`resources/read`), wrapped `<resource ref="…">…</resource>`.
- `@<path>` otherwise → a **local file or directory**, but only when the path
  actually exists on disk. This existence gate is the disambiguator: an ordinary
  `@mention` or an email address resolves to no file and stays literal text. A
  file is wrapped `<file path="…">…</file>` (size-capped, binary files noted not
  dumped); a directory becomes a recursive listing (depth-first, skipping common
  noise like `.git` and `node_modules`).
- Resolution is asynchronous (off the TUI event loop); a fetch failure surfaces
  as a notice but doesn't block the turn. Reads are user-initiated and read-only
  — they do **not** pass the permission gate (§3.7).
- Typing `/` or `@` opens an autocomplete menu above the input. The `@` menu
  navigates **one directory level at a time** (`os.ReadDir`, never a recursive
  walk — bounded for huge directories): a directory entry descends, a file
  completes, and MCP resources appear alongside top-level entries. The
  bottom-region menu changes height only on these discrete actions, never per
  streamed token, so scrollback stays clean (§ rendering).

### 3.10 Subagent profiles and explicit CLI execution

A subagent profile is a Skill with `runAs: subagent` and, for profiles managed
by the desktop or CLI editors, `invocation: manual`. Profiles reuse the existing
project/global Skill files; they do not introduce another state format or
database. Manual invocation excludes a profile from the pinned Skill index so
the model cannot discover it implicitly, while explicit `/<name> <task>`
invocation remains available.

Interactive slash invocation and `Controller.RunSubagentProfile` both execute
the profile with the Boot-wired Skill runners. Each run gets an isolated child
session and returns only its final answer to the caller. The headless contract is
explicit:

- `reasonix subagent try <name> ... <task>` uses the read-only Skill runner;
- `reasonix subagent run <name> ... <task>` uses the normal permission and
  sandbox path; and
- ordinary `Controller.Run` / `reasonix run` remains unchanged and does not
  reinterpret slash-prefixed input as a subagent command.

Desktop and CLI profile mutations share
`skill.ValidateEditableSubagentProfile`. Only simple manual project/global
profiles can be rewritten or deleted. Custom-scope Skills, unmanaged
frontmatter, and Skill directories containing `references/` or `scripts/` are
refused so an editor cannot silently flatten or discard rich Skill content.
Built-in profiles support configuration overrides but have no writable file.

Effective model and effort precedence is: per-profile
`agent.subagent_models` / `agent.subagent_efforts`, this call's `model` /
`effort` on `task`/`fleet`, profile frontmatter, `agent.subagent_model` /
`agent.subagent_effort`, then executor/default model configuration.

`task` accepts optional `profile` and `write_paths`. `fleet` dispatches 2–64
profile-aware tasks under a session scheduler
(`agent.max_subagent_concurrency`, default 6; `agent.max_parallel_writers`,
default 3). Profile names are resolved at runtime from the Skill store and
must never enter tool schemas or the parent system prompt. Custom and named
built-in profile bodies are the full child system prompt (no implicit
concise default). `parallel_tasks` remains the compatible read-only batch
API on the same scheduler. In a persisted parent session, parallel/fleet
children save independent transcripts; the aggregate carries bounded previews
and stable refs, and `read_subagent_result` pages a referenced final answer by
UTF-8 byte offset under the current conversation-lineage/workspace boundary.
Headless runs remain ephemeral and return fair bounded previews without refs.
See [Subagent profiles](./SUBAGENT_PROFILES.md)
for the user-facing command and file-format contract.

A profile describes a worker, not a run. Delegation is five separate concepts:
the profile says how a worker thinks, `TaskSpec` what this call wants,
`CapabilityGrant` what it may touch, `ContextCapsule` what it starts from, and
`SchedulerPolicy` when it runs. A field belongs to whichever member decides its
value, so a profile may carry a capability *ceiling* (`allowed-tools`,
`read-only`) but never a per-call value such as `max_turns`, `write_paths`, or a
retry or verification policy — those are decided by the task or the scheduler.
Skill frontmatter may keep growing; `agent.ProfileFromSkill` is the single
narrowing point, and routing metadata (triggers, auto-use, cost, freshness)
stops there because it decides *when* a worker is chosen, not how it thinks.
`internal/agent/profile_boundary_test.go` fails on any widening.

### 3.11 Sub-agents close with a host-adjudicated claim

A writer sub-agent ends its run by calling `complete_subtask` with a `status`,
a `summary`, the `acceptance_criteria` it was held to (each with the command it
ran or the paths it changed), and whatever it left `unresolved`. Prose alone is
still accepted, but it is no longer the interface the parent reasons over.

The submitted status is a claim, not a verdict. Before the parent sees it, the
host checks every citation against its own receipts: a `verification` criterion
must name a command the host recorded as run, `diff`/`files` must name paths the
host observed written or read, and a `manual` note is never self-backing. Any
criterion the receipts cannot back is lowered to `unsatisfied`, a report holding
one cannot stay `complete`, and the downgrade is printed with its reason. The
host never raises a status.

The parent therefore receives, in order: the adjudicated status and criteria,
the child's own prose, and the host's own receipts of what it changed and ran.

### 3.12 Write claims are enforced, not advisory

A declared `write_paths` is one truth source used for both scheduling and
enforcement. When a writer sub-agent declares explicit paths, the host binds its
registry to that claim before the child runs:

- path-aware built-in writers (`write_file`, `edit_file`, `multi_edit`,
  `move_file`, `notebook_edit`, `delete_range`, `delete_symbol`) reject any
  argument path outside the claim, with both ends of a `move_file` checked;
- paths are compared after symlink resolution against the deepest existing
  ancestor, so neither `..` traversal nor a symlink inside the claim can launder
  a write out of it;
- `bash` is kept only if the OS sandbox can rebind its write roots to the claim,
  and is otherwise removed from the child's registry entirely;
- MCP goes through `use_capability`, which refuses at resolve time — before any
  MCP process runs — every target not proven read-only;
- writers the host cannot path-scope (custom, unknown) are dropped;
- after the run, the host compares the mutations it recorded against the claim
  and reports any outside path to the parent in the sub-agent's host receipts.

Omitting `write_paths` is not an unscoped writer: the run claims the whole
workspace and therefore serialises against every other writer claim. That claim
is a scheduling boundary only — inside the workspace nothing is refused, because
no concurrent writer can hold an overlapping claim at the same time. Writes that
leave the workspace are still reported as claim violations.

Declaring paths is what buys parallelism; it costs `bash` on hosts where the OS
sandbox cannot enforce write roots.

### 3.13 Sub-agent context inheritance is explicit

A child inherits nothing implicitly. What it receives is exactly this:

| Given to the child | Where it comes from |
| --- | --- |
| System prompt | `DefaultTaskSystemPrompt`, `DefaultReadOnlyTaskSystemPrompt`, or the profile body — nothing else is composed into it |
| Workspace root | `<workspace-context>` on the first user turn |
| The task text | the user turn itself |
| Completion contract | appended to a writer's task turn (§3.11) |
| Delegation guidance | `<subagent-context>` on a nested child's fresh session |
| Plan-mode marker, reasoning/response language | run options, when set |
| A prior transcript | only via `continue_from` / `fork_from` |

Not inherited, by construction: `REASONIX.md`, `AGENTS.md`, `CLAUDE.md`, project
and global memory (the memory queue is disabled, so a child cannot record memory
either), the parent conversation, the current Goal, planner output, and sibling
sub-agent results. A constraint that must reach a child today has to be in its
profile body or in the task text — there is no ambient channel.

Every run records a `ContextCapsule` in its transcript sidecar: the workspace,
the system-prompt source and hash, the resolved tool scope and schema hash, the
model and effort, the parent session and tool-call id, any resumed transcript,
and an `inherited` block whose fields are all false. `capsuleHash` is its stable
identity, so *why did this reviewer not see that constraint* is answered from
the record, and two runs that behaved differently can be diffed instead of
guessed at. The capsule holds references and digests only — never copied parent
context, which is what keeps delegation cheap and the child prefix cacheable.

### 3.14 Fleet is a small dependency graph

A fleet item may declare `id` and `depends_on`. That is the whole graph
vocabulary: no conditions, no expressions, no dynamic fan-out. It is enough for

```
research ──▶ implement backend ──┐
        └──▶ implement frontend ─┴──▶ integration test ──▶ review
```

Ids default to the 1-based position. A duplicate id, an id no task declares, a
self-edge, or a cycle fails preflight, so a fleet that cannot finish never
starts. Items run as soon as their dependencies complete; items with no ordering
between them run in parallel under the same session scheduler as before.

Dependencies are a property of the graph, never of a task: they live in the
fleet plan and never reach `ProfileExecSpec`, which is what keeps `depends_on`
from becoming the first keyword of a workflow language.

The graph relaxes the write-claim preflight in the one place it should. Only
items that can run at the same time need disjoint `write_paths`; an
`implement → review` pair is serialised by its edge and may share paths, which
a flat fleet could not express.

Failure handling has one knob. A failed or skipped task always skips its whole
downstream branch — running a dependent on a broken input only buys a result the
parent must discard. Independent branches keep going unless `fail_fast` is set,
which stops *starting* new tasks; tasks already running are left to finish so a
writer is never abandoned mid-write.

### 3.15 One child-construction primitive

The APIs that spawn a child are many — `task`, `read_only_task`, `fleet`,
`parallel_tasks`, `run_skill`, `/<profile>`, `reasonix subagent run|try`,
desktop preview. The execution primitive behind them must stay one. Each entry
point compiles its request into a `ProfileExecSpec` and hands it to
`TaskTool.RunProfileSpec`, which is the only place that resolves depth, tool
scope, permissions, sandbox, write claims, scheduler slots, the MCP frontend,
the transcript and capsule, the evidence ledger, and the completion contract.

This is not a style preference. A safety boundary spread across several
construction paths only has to be forgotten once: past regressions where a
preview path built unconfined file tools, and where a profile editor dropped
`read-only` on save, were both one entry point missing one layer.

An entry point that must not persist a transcript says so with
`ContextRequest.Ephemeral` rather than building its own session, so its promise
is a field on the spec instead of a second construction path.

`internal/agent/spawn_boundary_test.go` enumerates the files that still call the
low-level runners directly and fails on any new one. The remaining entries —
`internal/boot` (skill runners), `internal/cli/review.go`, and
`desktop/subagents_app.go` — are known debt, not precedent.

### 3.16 MCP concurrency: read-only is not stateless

Sub-agents share one session Host and its connections while each keeps its own
`use_capability` frontend and ledger. For a stdio server that means they share
one process, and therefore its session state.

Read-only does not imply stateless. A browser server opens a page, selects a
tab, scrolls; every one of those tools may honestly declare `readOnly` because
nothing reaches the filesystem, yet two children calling it concurrently
interleave on state neither of them can see. Write claims do not help — there is
nothing to claim.

A configured server therefore carries a concurrency policy:

```toml
[[mcp.servers]]
name = "browser"
concurrency = "serial"   # parallel (default) | serial
```

`serial` means the runtime never runs two calls to that server at once across
the whole session, whichever child issues them. The gate lives on the shared
runtime because the process being interleaved on is shared at exactly that
scope, and a call waiting on it still honours its own cancellation. Servers
whose names look known-stateful (browser, playwright, puppeteer, chrome,
chromium, selenium) default to `serial`; explicit configuration always wins, and
everything else stays parallel so the shared-Host tradeoff is unchanged.

This is deliberately the conservative first version: one policy per server, not
per capability. Per-tool `parallel_safe` / `exclusive` hints and explicit
`concurrency_key` grouping are the later refinement, once real servers show
which tools within one server genuinely differ.

### 3.17 Measuring whether delegation pays

Orchestration is easy to add and hard to justify: more agents always cost more
tokens, and the extra tokens alone can look like an improvement. Comparing arms
therefore has to hold the model fixed and read host-recorded facts, not prose.

`reasonix run --json` emits per-run delegation counters alongside the existing
token, cache, cost, and duration totals:

| Counter | Answers |
| --- | --- |
| `subagent_runs`, `subagent_nested_runs` | which shape actually ran, not which was configured |
| `tool_calls` − `subagent_tool_calls` | parent versus child work split |
| `subagent_mutations`, `duplicate_work_paths` | did two children redo the same file |
| `completion_reports`, `completions_prose_only` | how much of the run ended in a checkable claim |
| `false_completions`, `criterion_downgrades` | claims the host refused to back |
| `write_scope_violations` | writes that escaped a declared claim |

The control axis is partial, and the counters are what revealed it.
`--ablate subagent` removes `task`, `read_only_task`, `fleet`, and
`parallel_tasks`, but a run can still delegate through a `runAs=subagent`
profile skill: a measured `no-subagent` arm spent a child run on `explore`.
Treat that arm as "no task-tool delegation", not "single agent", and read
`subagent_runs` to see what actually happened rather than trusting the label.
Nested depth is `agent.max_subagent_depth`.

`false_completions` is the counter that matters most. It comes from the
adjudication in §3.11, so it measures claims the host refused rather than a
reviewer's opinion, and it is the one number that separates "the fleet finished
faster" from "the fleet said it finished".

Read these against the measured noise floor. Running the same arm twice over
the same tasks moved per-task token use by a median of 19% and up to 54%, while
the whole between-arm difference in that experiment was 2.5%. A single run per
cell therefore proves nothing about delegation: the effect has to clear the
variance before it is an effect. Budget repetitions, or restrict the comparison
to tasks where `subagent_runs` shows delegation actually happened — in that
experiment it happened on one task in six.

What the counters have measured so far, on one model over four task shapes,
each comparing a neutral prompt against a forced-delegation twin over identical
work: three one-line fixes in separate modules cost 3.8x the tokens; a 24-file
search 1.5x tokens and 2.2x wall; a 36-file three-package migration 2.6x tokens
and 4.1x wall; three genuinely heterogeneous branches, the shape with the best
theoretical case, 2.4x tokens and 3.7x wall over three repetitions. Success rate
was 100% everywhere, and the forced arm's spread was about twice the neutral
arm's, so delegation also buys variance.

Read a child's token figure carefully: 27 measured child runs averaged 134k
tokens each, but that is cumulative prompt tokens over 9.3 model calls with the
same ~14k context re-sent each time, not 134k tokens of new material. At ~90%
cache hit the real price of a child averaged ¥0.017. The 2-4x above is the
number that matters, because both arms are counted the same way; the per-child
total is not a threshold to compare a branch's size against.

Why delegation is rare is answerable from the same runs, and the answer is not
that the model weighs it and declines. Across 33 runs with delegation available,
15% delegated and bash outnumbered every delegation-class call 10:1. The
recorded reasoning shows the model deliberating over how to read efficiently —
"that's 25 files... read them in parallel batches... I can read multiple files
at once" — on a task built for `explore`, without delegation entering the
decision at all.

Three things explain that, and only one of them is a defect. The base system
prompt never mentions delegation; every mention lives in the skills index, and
each is a brake ("the heavy path... only when the task genuinely needs
context-heavy work, not on weak relevance") next to an accelerator for inline
skills ("even plausibly relevant... cheap"). The `task` tool description says
what the tool does and never when to reach for it. And the model already has
cheaper parallelism — several tool calls in one round trip, with no context
duplicated — which is what it reasons in terms of.

Given the measured 2.4-4.5x, a brake is the correct default; the gap is that
nothing recognises the rare case where delegation would pay. Forcing it does not
close that gap: in the forced fleet run the parent worked out all three fixes in
its own reasoning before dispatching, so the children re-read the code to apply
edits the parent had already derived. Delegation moved the typing, not the
thinking.

One hypothesis remains untested rather than disproved: delegation's isolation
should pay when the parent is actually hurt by what it read. It could not be
provoked here. Pinning a workspace `compact_ratio` down to 0.5% still produced
zero compactions, because the agent keeps its session small by writing a script
instead of reading — the same behaviour that wins it the comparisons. Context
pressure needs a task that cannot be scripted away, which this corpus does not
yet contain.

The migration is the instructive one. Left alone the agent read a single file,
wrote a script and changed 108 call sites in 28 seconds; split across three
packages, no branch could see the transformation that solved all three. A task
looking parallel-shaped is not evidence that splitting it is cheaper.

Not yet measured, and deliberately not faked: rework-after-handoff needs
mutation ordering across a whole run, which belongs to the harness driving the
arms rather than the instrument recording one.

## 4. Data Types (`internal/provider`)

```go
type Role string
const (RoleSystem Role = "system"; RoleUser Role = "user"
       RoleAssistant Role = "assistant"; RoleTool Role = "tool")

type Message struct {
    Role       Role       `json:"role"`
    Content    string     `json:"content,omitempty"`
    ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
    ToolCallID string     `json:"tool_call_id,omitempty"`
    Name       string     `json:"name,omitempty"`
}

type ToolCall   struct { ID, Name, Arguments string }              // Arguments: raw JSON
type ToolSchema struct { Name, Description string; Parameters json.RawMessage }
type Request    struct { Messages []Message; Tools []ToolSchema; Temperature float64; MaxTokens int }

type ChunkType int
const (ChunkText ChunkType = iota; ChunkToolCall; ChunkDone; ChunkError)

type Chunk struct {
    Type     ChunkType
    Text     string    // ChunkText
    ToolCall *ToolCall // ChunkToolCall
    Err      error     // ChunkError
}
```

## 5. Configuration (TOML)

Resolution order: **flag > project `./reasonix.toml` > the user config file
> built-in defaults**. Starting with **Reasonix v1.8.1**, the user config lives
at `~/.reasonix/config.toml` on macOS/Linux and
`%AppData%\reasonix\config.toml` on Windows. See
[Configuration paths](./CONFIG_PATHS.md) for migration and related data paths.
Fields marked user/global only are not overridden by project `reasonix.toml`.
Provider entries name secrets with `api_key_env`; saved key values live in
Reasonix's global `<Reasonix home>/.env`, shared by CLI and desktop. Project
`.env`, home `.env`, inherited shell environment variables, legacy credentials,
and the OS keyring are not provider-key runtime fallbacks. Project `.env` still
feeds workspace-scoped, non-provider `${VAR}` expansion for MCP/plugin settings
without importing provider keys or Reasonix control variables.

```toml
default_model = "deepseek"   # provider name (→ its default model) or "provider/model"
# language    = "zh"                # ui language tag; empty = auto-detect from $LANG / $REASONIX_LANG

[ui]
# shortcut_layout = "desktop"       # classic|desktop; compatibility setting
# cursor_shape = "bar"              # CLI/TUI textarea cursor: underline|block|bar
show_turn_usage = false              # hide per-request token/cost receipts in the TUI; default true

[agent]
system_prompt = "You are Reasonix, a coding agent..."  # or system_prompt_file = "..."
temperature       = 0.0
reasoning_language = "auto"       # visible reasoning text: auto|zh|en
# plan_mode_read_only_commands = ["gh issue view"]   # legacy compatibility only; Plan bash uses Permissions
# planner_model = "deepseek-pro"   # optional: two-model collaboration (low-frequency planner)
# subagent_model = "deepseek-pro"   # optional default for runAs=subagent skills
# subagent_effort = "high"           # optional default reasoning effort for subagents
# subagent_models = { review = "deepseek-pro", security_review = "deepseek-pro" }
# subagent_efforts = { review = "max", security_review = "high" }

# A vendor endpoint exposing several models under one base_url/key.
[[providers]]
name           = "deepseek"
kind           = "anthropic"
base_url       = "https://api.deepseek.com/anthropic"
# request_url  = "https://proxy.example.com/anthropic/v1/messages" # optional exact provider request URL
# models_url   = "https://proxy.example.com/v1/models"             # optional model discovery URL
models         = ["deepseek-v4-flash", "deepseek-v4-pro"]
default        = "deepseek-v4-flash"   # optional; defaults to models[0]
api_key_env    = "DEEPSEEK_API_KEY"
web_search     = true
context_window = 1000000   # tokens; harness compacts older history near this limit (0 disables)
# max_output_tokens = 0              # auto: provider capability; official DeepSeek omits until the window is tight
# max_output_tokens = 32768          # optional cost cap; still clipped to physical remaining
# max_output_tokens = 65536          # optional cost cap
# max_output_tokens = -1             # force-omit optional wire limits; compact if the auto budget no longer fits
# max_output_tokens never changes compact_ratio
# model_overrides = { "deepseek-v4-flash" = { context_window = 1000000, max_output_tokens = 32768 } }

# A single-model entry still works for custom OpenAI-compatible endpoints.

[environment]
enabled = true   # inject a stable startup summary of OS, shell, and common tool versions
offline = false  # set true when outbound network access is unavailable; prevents futile retries

# Optional trusted executable paths shown to the model when PATH probing is not enough.
# Workspace-local paths are listed but not auto-executed during startup probing.
# [environment.tools]
# go = "/opt/homebrew/bin/go"

[tools]
enabled = []   # omit/empty = all built-ins
bash_timeout_seconds = 120   # foreground safety cap; set 0 for no tool-local cap
mcp_startup_timeout_seconds = 30   # background initialize + tools/list safety cap
mcp_call_timeout_seconds = 300   # default MCP call safety cap; plugin/tool overrides may raise it

[tools.shell]
prefer = "auto"   # auto (default) | bash | powershell | pwsh — force the shell tool's interpreter
# path = "C:\\Program Files\\PowerShell\\7\\pwsh.exe"   # explicit executable for the chosen shell

[skills]
# paths = ["~/my-skills", "../shared/skills"]   # extra custom skill roots
# excluded_paths = ["~/.agents/skills"]         # hide convention roots without deleting folders
# disabled_skills = ["review"]                  # hidden from prompt, slash invocation, and skill tools

[permissions]
mode  = "ask"                              # writer fallback when no rule matches: ask|allow|deny
deny  = ["Bash(rm -rf*)", "Bash(git push*)"]   # hard-blocked in every mode
allow = ["Bash(go test:*)", "Bash(git status:*)"]  # never prompted
ask   = []                                 # force a prompt even if otherwise allowed

[sandbox]
# workspace_root = ""          # file-writers confined here; empty = cwd
# allow_write    = ["/tmp"]    # extra dirs write_file/edit_file/multi_edit/move_file may modify
# forbid_read    = ["${HOME}/.ssh"]   # paths read/list/search tools and sandboxed bash may not inspect

[serve]
auth_mode = "none"             # none|token|password; use auth before binding beyond localhost
# token = ""                   # optional fixed token; empty token mode generates one at startup
# password_hash = ""           # bcrypt hash generated with reasonix serve --hash-password --password '...'
# behind_proxy = false         # trust X-Forwarded-* only behind a trusted reverse proxy

[[plugins]]
name    = "example"            # type defaults to "stdio"
command = "reasonix-plugin-example"
args    = []
# env   = { FOO = "bar" }
# startup_timeout_seconds = 60         # initialize + tools/list cap; 0 = global/default cap
# call_timeout_seconds = 600            # per-server MCP call timeout; 0 = global/default cap
# tool_timeout_seconds = { "generate_video" = 1800 }   # raw MCP tool names
# [[plugins]]                   # a remote MCP server over Streamable HTTP
# name    = "stripe"
# type    = "http"             # "stdio" (default) | "http" | "sse"
# url     = "https://mcp.stripe.com"
# headers = { Authorization = "Bearer ${STRIPE_KEY}" }   # ${VAR} / ${VAR:-default} expanded
```

The native CLI updater always installs the latest strict `vX.Y.Z` official
release. Legacy channel configuration and arguments remain parseable during
1.x, resolve to the official release, and are omitted on subsequent writes.

The executor tracks an adaptive progress lease while a todo is active. A new
completion, unique successful read, command, or mutation renews the lease;
exact repeats do not. After 8 no-progress tool-call rounds the host appends a
one-shot reassessment nudge. In Goal mode, the later threshold forces a re-plan
and continues; outside Goal it may end the current attempt. The serial contract is level-aware while preserving the
single-in_progress rule: in a two-level list the active level-1 sub-step is
the only `in_progress` item and its level-0 phase stays `pending`; sub-steps
complete in order, and the phase becomes `in_progress` — and signs off — only
after all of its sub-steps have completed. A level-1 item with no phase above
it is rejected. Retired `[agent].max_steps` and `planner_max_steps` keys remain
parseable for upgrade compatibility, but are ignored and removed by a one-time
migration. The CLI `--max-steps` flag and `[bot].max_steps` remain separate,
explicit controls for one-off and unattended execution; bot `0` means continuous.

`reasonix setup` writes this default config so the CLI is usable out of the box.

`[ui].cursor_shape` is normalized to `underline`, `block`, or `bar`; empty or
unknown values fall back to `bar`. It applies to the Bubble Tea CLI/TUI
textarea only, while desktop and browser inputs keep their platform-native
cursor behavior.

`[serve]` controls the HTTP browser frontend used by `reasonix serve`. The
default `auth_mode = "none"` is intended for the loopback default
`127.0.0.1:8787`; deployments reachable from another machine must use `token` or
`password`. Password mode requires either a startup `--password` or a stored
bcrypt `password_hash`. `behind_proxy` must stay false unless the server is
behind a trusted proxy that owns the `X-Forwarded-For` and `X-Forwarded-Proto`
headers.

MCP servers may also be declared in a project-root `.mcp.json` using Claude
Code's exact `mcpServers` schema (`command`/`args`/`env`, `type`/`url`/`headers`,
`${VAR}` expansion). It is read after the TOML files and merged into
`[[plugins]]`; on a name collision `reasonix.toml` wins (it is the more explicit,
Reasonix-specific source). This lets a server already configured for Claude work in
Reasonix unchanged.

MCP startup has a separate lifecycle from an individual tool call. A caller
waits briefly for cold startup, while the shared launch/authorization/
`initialize`/`tools/list` sequence may continue in the background up to
`mcp_startup_timeout_seconds` (default `30`). A per-server
`startup_timeout_seconds` overrides that cap. MCP call timeouts begin only after
the connection is ready.

```json
{ "mcpServers": {
  "stripe": { "type": "http", "url": "https://mcp.stripe.com",
              "headers": { "Authorization": "Bearer ${STRIPE_KEY}" } }
} }
```

`[sandbox]` is the *enforcement* layer beneath permissions (which are *policy*).
They stay two layers: a permitted call still cannot write outside the approved
roots. Interactive sessions can extend those roots with a write-access approval
(once / session / project `reasonix.toml` / deny). File tools request the target
parent directory automatically. Bash must declare `additional_write_dirs` and a
`justification`; the host does not infer paths from the command text. Headless
`reasonix run` fails closed unless the directory is already in
`[sandbox].allow_write` or `--add-dir`. Granting `${HOME}` is allowed with a
high-risk warning; the filesystem root and Reasonix session/state paths are not.
Phase 0 confines the file-writing built-ins (`write_file`, `edit_file`,
`multi_edit`, `move_file`) to `workspace_root` (default cwd), the Reasonix user
config dir, plus `allow_write`: a write whose target — resolved to an absolute,
symlink-free path so a symlinked dir or `..` cannot tunnel out — falls outside
every root is refused, and the error is fed back to the model. Confinement is on
by default (root = cwd), so edits stay in the project while the agent can still
update its own global config. `forbid_read` lists files or directories the agent should
not read, list, or search; entries support `${VAR}` / `${VAR:-default}` expansion
and should be absolute, or use `${HOME}` for home-relative secrets such as
`${HOME}/.ssh`. `bash` is itself jailed by default when an OS sandbox is
available (`[sandbox] bash = "enforce"`: Seatbelt on macOS and bubblewrap on
Linux): each command is allowed to write only
the same roots plus platform-specific command temp/cache roots, denied reads
under `forbid_read`, and allowed to reach the network only when
`network = true`.
**Windows status:** Reasonix does not ship an OS-level Bash sandbox on Windows.
The effective mode is fixed to `off`; an older config containing
`bash = "enforce"` remains readable but resolves to `off`, `reasonix doctor`
reports the ignored value, and the desktop control is read-only. Bash therefore
runs unconfined on Windows. The in-process file tools continue to enforce
`workspace_root`, `allow_write`, and `forbid_read`.
When no OS sandbox is available, `bash = "enforce"` refuses bash execution
instead of running unconfined. Install the platform sandbox backend
(bubblewrap/`bwrap` on Linux, `sandbox-exec` on macOS) or set
`[sandbox] bash = "off"` to explicitly restore the pre-1.16 unconfined shell
behavior. The escape-prompt and broader OS support are Phase 1's remainder (§9).

## 6. Error Handling

- Library code wraps with `fmt.Errorf("...: %w", err)` and returns; it never
  prints or calls `os.Exit`.
- Only `cli` / `main` decide exit codes and user-facing messages.
- Tool execution errors are fed back to the model, not fatal.
- Network layer should apply bounded exponential backoff on 429 / 5xx
  (interface reserved; implementation may follow).

## 7. Code Style

- `gofmt` + `go vet` must be clean; package names lowercase; exported
  identifiers documented; comments explain *why*, not *what*.
- No premature generalization. Prefer clear and direct.

## 8. Distribution

- Build: `CGO_ENABLED=0 go build -ldflags "-s -w -X main.version=$(VERSION)" -o reasonix ./cmd/reasonix`
- Cross matrix: `darwin|linux|windows` × `amd64|arm64`.
- Version injected via ldflags (`git describe --tags --always`).
- Install: prebuilt binary / `go install` / future `brew tap`.

## 9. Roadmap (not in current scope)

- Sandbox Phase 1: an OS-level jail for `bash` so commands — not just the
  file-writer built-ins (Phase 0) — are confined to the workspace. **Seatbelt on
  macOS and bubblewrap on Linux ship, on by default when available** (see §5).
  Remaining: the escape-prompt — detect sandbox-unavailable or sandbox-denied failures and
  offer an explicit, permission-gated unconfined rerun (in `reasonix run`, the
  command just fails and the model adapts), which completes the "allow inside the
  box, prompt at its edge" model. With this in place, "always allow" rule
  persistence becomes optional rather than load-bearing.
- MCP long tail (deferred deliberately): `headersHelper` auth for remote
  servers; the remaining `.mcp.json` scopes
  (local / user — project scope shipped, see §5); tool-search deferral;
  `list_changed` live updates; channels / elicitation / roots; plugins that
  provide *providers*, not just tools.
- An Anthropic-native provider `kind` (native prompt-cache control), proving the
  registry generalises beyond one wire format.
- "Always allow" persistence writing learned rules back to project config; a
  per-session permission override flag for `reasonix run`.