feat(S-603): Create docs/architecture.md
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# ai-cli-dispatch Architecture
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This document describes the internal design of `ai-cli-dispatch`, the module breakdown, data flow, key design decisions, and how to extend the tool.
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## Module Breakdown
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```text
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src/
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├── cli.ts — Entry point: argument parsing, command routing, I/O formatting
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├── types.ts — Shared types and error classes
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├── constants.ts — Client name registry and platform helpers
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├── config.ts — Layered configuration resolution (flags → env → file → PATH)
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├── detect.ts — Client discovery: binary lookup and version extraction
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├── dispatch.ts — Prompt-to-client resolution (explicit flag → keywords → default)
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└── execute.ts — Subprocess spawning, stdout/stderr capture, timeout handling
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```
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### Responsibilities
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| Module | Responsibility |
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|---|---|
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| `cli.ts` | Parses `argv` with `minimist`, routes to `list` / `run` / `dispatch`, prints JSON or text output, and controls the process exit code. |
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| `types.ts` | Defines `ClientName`, `ClientInfo`, `ExecResult`, `ToolConfig`, and the error hierarchy (`ClientNotFoundError`, `ExecError`). |
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| `constants.ts` | Holds the canonical `CLIENT_NAMES` array and `isWindows()` helper used by discovery and config. |
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| `config.ts` | Resolves per-client binary paths and the optional `defaultClient` from four layered sources. |
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| `detect.ts` | Locates each client binary on `PATH`, falls back to a manual directory scan, and invokes `--version` to extract a semver string. |
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| `dispatch.ts` | Chooses the target client from a prompt string using ordered keyword matching, with overrides for explicit `--client` and `defaultClient`. |
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| `execute.ts` | Spawns the chosen client with its native argument shape, buffers `stdout`/`stderr`, enforces a timeout, and returns an `ExecResult` or throws a typed error. |
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## Data Flow
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A typical `dispatch` invocation flows through four stages:
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```
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┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐
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│ detect │ ──► │ config │ ──► │ dispatch │ ──► │ execute │
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└─────────────┘ └─────────────┘ └─────────────┘ └─────────────┘
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│ │ │ │
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which/where flags/env/file keyword scan spawn child
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PATH walk defaultClient --client override capture output
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--version fallback default timeout / exitCode
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```
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### 1. Detect
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`detectClients()` iterates over `CLIENT_NAMES` and attempts to locate each binary:
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1. Invoke `which <name>` (or `where <name>` on Windows).
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2. If that fails, walk `PATH` segments manually and test `existsSync()`.
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3. If a binary is found, run `<binary> --version` and parse the first semver-like match.
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Result: an array of `ClientInfo` objects with `name`, `found`, `path`, and `version`.
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### 2. Config
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`resolveConfig()` builds a `ResolvedConfig` by layering sources (highest to lowest precedence):
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1. **CLI flags** — `--codex-path`, `--claude-path`, `--opencode-path`, `--default-client`
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2. **Environment variables** — `AI_CLI_CODEX_PATH`, `AI_CLI_CLAUDE_PATH`, `AI_CLI_OPENCODE_PATH`, `AI_CLI_DEFAULT_CLIENT`
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3. **Config file** — `~/.openclaw/ai-cli-dispatch.json` (`paths` and `defaultClient` keys)
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4. **PATH discovery** — `which`/`where` fallback via `defaultWhichSync()`
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Only values for the three known `ClientName` entries are accepted; unknown `defaultClient` values are ignored.
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### 3. Dispatch
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`resolveClient(prompt, config)` decides which client to use:
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1. If `config.client` is a valid `ClientName`, return it immediately.
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2. Lower-case the prompt and scan for substrings in order:
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- `"open code"` → `opencode`
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- `"claude"` → `claude`
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- `"codex"` → `codex`
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- `"opencode"` → `opencode`
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3. If no keyword matches, return `config.defaultClient` or `null`.
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This ordering intentionally prioritizes `"open code"` before `"opencode"` so the spaced natural-language variant wins.
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### 4. Execute
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`executePrompt(client, prompt, options)` runs the selected client:
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1. Reject empty or whitespace-only prompts with `ExecError`.
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2. Validate that an explicit `clientPath` exists on disk (if provided).
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3. Map the client to its native argument array via `CLIENT_ARGS`:
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- `codex` → `["exec", prompt]`
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- `claude` → `["-p", prompt]`
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- `opencode` → `[prompt]`
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4. `spawn()` the process with `shell: false`.
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5. Buffer `stdout` and `stderr` via `"data"` listeners.
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6. Start a `setTimeout`; if it fires, `child.kill()` is sent.
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7. On `close`, resolve with `{ stdout, stderr, exitCode }`.
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8. On `error`, reject with `ClientNotFoundError` for `ENOENT` or `ExecError` for anything else.
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9. On timeout, reject with `ExecError` containing the buffered output so far.
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The default timeout is **5 minutes** (`300_000` ms).
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## Design Decisions
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### Coexistence with ACP
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`ai-cli-dispatch` is intentionally **not** an ACP agent. It is a thin, local subprocess wrapper with no session state, no thread binding, and no orchestrator protocol.
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- Use `ai-cli-dispatch` when you need a quick, one-shot CLI execution on the gateway host.
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- Use ACP (`docs/openclaw-acp-orchestration.md`) when you need session-bound coding harnesses, multi-turn review, or orchestrator-managed verification gates.
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This separation keeps the dispatcher small and avoids duplicating ACP’s scheduling, context persistence, and review-loop responsibilities.
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### Keyword Dispatch vs NLP
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Client resolution uses deterministic substring matching instead of natural-language parsing or an LLM call.
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**Rationale:**
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- **Speed:** No network round-trip or model load; resolution is synchronous and sub-millisecond.
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- **Predictability:** The same prompt always resolves to the same client. There is no temperature, context window, or model-version drift.
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- **Debuggability:** A user can read the ordered keyword list and know exactly why a given prompt resolved to a given client.
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- **Scope fit:** The dispatcher only needs to distinguish three clients. A full NLP pipeline would be overkill.
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The trade-off is that prompts like `"compare codex and claude"` resolve to `codex` because `"codex"` is checked first. Users can always override with `--client`.
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### Sync-Only Initial Release
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The current implementation is entirely synchronous from the caller’s perspective: `executePrompt` returns a promise that resolves only when the child process exits or the timeout fires.
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**Rationale:**
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- The primary use case is one-shot tasks (refactor, add tests, migrate) where the agent needs the complete output before proceeding.
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- Streaming would require a different output contract (callbacks, generators, or an event emitter) and complicates the JSON error model.
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- ACP already covers interactive, streaming, and session-based use cases.
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Streaming is an intentional future extension point (see below).
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### Error Taxonomy
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All runtime failures are represented as typed errors so callers and tests can branch precisely:
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| Error | When thrown | Data carried |
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|---|---|---|
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| `ClientNotFoundError` | Binary not on `PATH`, explicit `clientPath` missing, or `ENOENT` from `spawn` | `message` with client name |
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| `ExecError` | Empty prompt, unknown client, timeout, non-`ENOENT` spawn error, or child exit | `message` + full `ExecResult` (`stdout`, `stderr`, `exitCode`) |
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`ExecError` carries the `ExecResult` so that timeout handlers still return partial output. This avoids losing buffered stdout/stderr when a long-running task is killed.
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### Injection-Friendly Module Boundaries
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Every non-trivial module accepts an `options` bag with injectable dependencies (`spawnSync`, `spawn`, `existsSync`, `whichSync`, `readFileSync`, etc.).
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**Rationale:**
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- Unit tests can run without touching the real filesystem, `PATH`, or subprocess layer.
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- The CLI itself injects its real dependencies through default parameters, so production behavior is unchanged.
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- There is no global mocking required; each test provides its own narrow fakes.
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### Minimal Dependency Surface
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The runtime dependency graph contains exactly one external package: `minimist` (argument parsing). Everything else uses Node.js built-ins (`child_process`, `fs`, `os`, `path`).
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**Rationale:**
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- Reduces supply-chain risk and install time.
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- Avoids version-lock issues across Node.js 20+ environments.
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- Keeps the compiled/bundled footprint negligible for a tool that is often installed as a sidecar.
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## Extension Points
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### Adding a New Client
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To support a fourth (or fifth) AI CLI client, change four files in `src/` and the corresponding tests:
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1. **`src/types.ts`** — Add the new name to the `ClientName` union type.
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2. **`src/constants.ts`** — Append the new name to `CLIENT_NAMES`.
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3. **`src/execute.ts`** — Add an entry to `CLIENT_ARGS` with the client’s native argument shape.
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4. **`src/config.ts`** — No change required; the existing loop over `CLIENT_NAMES` automatically picks up the new env/flag/file keys.
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5. **`src/dispatch.ts`** — Add a keyword check for the new client in `resolveClient`. Decide its precedence relative to existing keywords.
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6. **Tests** — Add colocated test cases in `tests/dispatch.test.ts`, `tests/execute.test.ts`, and `tests/detect.test.ts`.
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No changes are needed in `cli.ts` because it iterates over `CLIENT_NAMES` for validation.
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### Streaming Support
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If a future use case requires real-time output (e.g., long-running codegen with progressive feedback), the cleanest extension is to add an optional `onData` callback to `ExecuteOptions`:
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```typescript
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export interface ExecuteOptions {
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clientPath?: string;
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timeoutMs?: number;
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spawn?: ...;
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existsSync?: ...;
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onData?: (chunk: string, stream: "stdout" | "stderr") => void;
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}
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```
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When `onData` is provided, `executePrompt` would:
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- Continue buffering internally for the final `ExecResult`.
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- Also emit each chunk through `onData` so the caller can stream to a UI or logger.
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- Reject/resolve with the same error taxonomy.
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This preserves backward compatibility: existing callers that omit `onData` receive the exact same buffered `ExecResult` they get today.
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### Platform Backends
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The current Windows support is limited to discovery (`where` instead of `which`, `.exe` extension assumptions). If future clients require platform-specific spawn options (e.g., PowerShell quoting rules), the extension point is `CLIENT_ARGS` or a new `CLIENT_SPAWN_OPTIONS` record keyed by `ClientName`.
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## Testing Strategy
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The test suite in `tests/` mirrors the `src/` structure:
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| Test file | Coverage |
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| `cli.test.ts` | Argument parsing, command routing, JSON/text output modes, exit codes, error formatting |
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| `config.test.ts` | Layered precedence of flags, env, file, and `which` fallback; malformed JSON tolerance |
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| `detect.test.ts` | `which` success/failure, PATH directory fallback, version parsing, missing binary handling |
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| `dispatch.test.ts` | Keyword matching, case insensitivity, `--client` precedence, `defaultClient` fallback, invalid flag handling |
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| `execute.test.ts` | Successful execution, stderr capture, non-zero exit codes, `ENOENT` → `ClientNotFoundError`, timeout, empty prompt rejection, special-character preservation |
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All tests use injected mocks; no test spawns real client binaries or reads the real filesystem.
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