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+# ADR-007: Built-in tools and workspace sandboxing
+
+**Status:** Proposed
+**Date:** 2026-03-31
+
+---
+
+## Context
+
+ADR-005 defines tool execution as spawning plugin executables with JSON on
+stdin/stdout. This works well for third-party and optional tools, but every
+agent needs a baseline set of filesystem tools to be useful — reading files,
+editing code, searching content. These operations happen on nearly every LLM
+turn and must be fast.
+
+Coding agents (Claude Code, Cursor, Windsurf) have converged on a common tool
+set: read, edit, grep, glob, bash. This is not a coincidence — these tools map
+directly to what a developer does in a terminal, and LLMs are trained on
+enormous amounts of terminal interaction. Providing the same primitives to loom
+agents gives them the same capabilities.
+
+The second question is scope: what can an agent's tools access? An unsandboxed
+agent with `read` and `bash` can access anything the host user can. This is
+fine for a developer sitting at a terminal, but not for a managed agent running
+in the background. We need a default boundary.
+
+## Decision
+
+### Built-in tools
+
+The runner includes six built-in tools implemented as functions inside the
+runner process. They are always available to every agent. No subprocess is
+spawned — tool calls execute in-process for minimal latency.
+
+| Tool | Purpose | Key parameters | Default |
+|------|---------|----------------|---------|
+| **read** | Read file contents | `path`, `offset`, `limit` | enabled |
+| **write** | Create or overwrite a file | `path`, `content` | enabled |
+| **edit** | Replace a string in an existing file | `path`, `old_string`, `new_string` | enabled |
+| **glob** | Find files matching a pattern | `pattern`, `path` | enabled |
+| **grep** | Search file contents by regex | `pattern`, `path`, `glob` | enabled |
+| **bash** | Execute a shell command | `command`, `timeout` | disabled |
+
+All built-in tools except bash are enabled by default. Any built-in tool can
+be disabled per-agent via configuration:
+
+```yaml
+# loom.yml
+agents:
+  researcher:
+    model: anthropic/claude-sonnet-4-20250514
+    tools:
+      bash: true          # opt-in
+      write: false        # opt-out
+      edit: false          # opt-out — read-only agent
+```
+
+```sh
+# CLI overrides
+loom run --name researcher --model anthropic/claude-sonnet-4-20250514 \
+  --enable-tool bash --disable-tool write --disable-tool edit
+```
+
+Disabled tools are excluded from the schema sent to the LLM — the model
+doesn't know they exist.
+
+Built-in tools use the same JSON Schema interface that plugins use (see
+ADR-005). The runner generates their tool definitions and merges them with any
+plugin tool definitions before sending the combined list to the LLM.
+
+#### read
+
+Reads file contents with optional offset and line limit. Returns content with
+line numbers. Can read text files, and when supported by the LLM, images and
+PDFs.
+
+```json
+{
+  "name": "read",
+  "parameters": {
+    "path": "src/index.ts",
+    "offset": 0,
+    "limit": 200
+  }
+}
+```
+
+Returns the file content as a string with line numbers prefixed.
+
+#### write
+
+Creates a new file or overwrites an existing file. Creates parent directories
+if they don't exist.
+
+```json
+{
+  "name": "write",
+  "parameters": {
+    "path": "src/config.ts",
+    "content": "export const PORT = 3000;\n"
+  }
+}
+```
+
+#### edit
+
+Performs exact string replacement in an existing file. The `old_string` must
+match exactly one location in the file (unless `replace_all` is set). This is
+safer than write for modifications — it prevents accidentally overwriting
+unrelated content.
+
+```json
+{
+  "name": "edit",
+  "parameters": {
+    "path": "src/config.ts",
+    "old_string": "const PORT = 3000",
+    "new_string": "const PORT = 8080",
+    "replace_all": false
+  }
+}
+```
+
+Fails if `old_string` is not found or matches multiple locations (when
+`replace_all` is false).
+
+#### glob
+
+Finds files matching a glob pattern. Returns file paths sorted by modification
+time. Useful for discovering project structure.
+
+```json
+{
+  "name": "glob",
+  "parameters": {
+    "pattern": "**/*.ts",
+    "path": "src"
+  }
+}
+```
+
+#### grep
+
+Searches file contents using regular expressions. Supports filtering by file
+glob and limiting output.
+
+```json
+{
+  "name": "grep",
+  "parameters": {
+    "pattern": "function\\s+handle",
+    "path": "src",
+    "glob": "*.ts"
+  }
+}
+```
+
+Returns matching lines with file paths and line numbers.
+
+#### bash
+
+Executes a shell command and returns stdout, stderr, and exit code. The command
+runs in the agent's workspace directory with the agent's environment variables.
+
+```json
+{
+  "name": "bash",
+  "parameters": {
+    "command": "bun test --filter auth",
+    "timeout": 30000
+  }
+}
+```
+
+Bash is **opt-in** — disabled by default, enabled per-agent via configuration.
+When disabled, the tool is not included in the schema sent to the LLM. The
+operator assumes responsibility for what the agent can do with shell access.
+
+### Workspace sandboxing
+
+Every agent has a **workspace** — a directory that its built-in tools are
+scoped to. All paths passed to built-in tools are resolved relative to the
+workspace. Path traversal outside the workspace is rejected.
+
+```
+read("src/index.ts")           → OK (relative to workspace)
+read("/etc/passwd")            → REJECTED (absolute path outside workspace)
+read("../../etc/passwd")       → REJECTED (traversal outside workspace)
+```
+
+#### Default workspace paths
+
+| Mode | Default workspace | Override |
+|------|-------------------|----------|
+| `loom run` (foreground) | Current working directory (`cwd`) | `--workspace /path` |
+| `loom run --detach` | `$LOOM_HOME/agents/{name}/workspace/` | `--workspace /path` |
+| `loom up` (via `loom.yml`) | `$LOOM_HOME/agents/{name}/workspace/` | `workspace:` key in `loom.yml` |
+
+The foreground default of `cwd` is intentional: you `cd` into a project and
+run an agent against it, just like running any other CLI tool.
+
+For managed agents, the workspace is a dedicated directory inside the agent's
+home. This prevents managed agents from accidentally modifying the operator's
+files. The operator can override this to point at a project directory when they
+want the agent to work on real files.
+
+#### Workspace vs agent directories
+
+The workspace is **separate from the agent's internal directories**:
+
+```
+$LOOM_HOME/agents/{name}/
+  pid
+  status
+  model
+  inbox/
+  outbox/
+  logs/
+  plugins/            ← plugin scoped directories (plugins/{plugin_name}/)
+  workspace/          ← built-in tools are scoped here
+```
+
+Built-in tools cannot access `inbox/`, `outbox/`, `logs/`, or other agent
+internals. These are managed by the runner and by plugin tools with explicit
+access grants.
+
+### Plugin tools and scoped directories
+
+Plugin tools (ADR-005) operate on their own scoped directories, separate from
+the workspace. The plugin declares the directory it needs; the runner creates
+it and passes the path at invocation.
+
+```
+$LOOM_HOME/agents/{name}/
+  plugins/
+    memory/           ← memory plugin's scoped directory
+    browser/          ← browser plugin's scoped directory
+  workspace/          ← built-in tools' scope
+```
+
+All plugin directories live under `plugins/{plugin_name}/`. The runner creates
+the directory on first use and passes the path at invocation.
+
+For example, a **memory** plugin:
+- The runner creates `$LOOM_HOME/agents/{name}/plugins/memory/` and passes it
+  as `scope_dir` in the plugin's invocation JSON
+- The plugin reads/writes within its scoped directory
+- By default, the plugin cannot see `workspace/`
+
+#### Plugin workspace access
+
+Plugins can be configured to also receive access to the agent's workspace.
+This is opt-in per plugin — the operator grants it in the agent or weave
+configuration:
+
+```yaml
+# loom.yml
+agents:
+  researcher:
+    model: anthropic/claude-sonnet-4-20250514
+    plugins:
+      memory: {}                          # scoped dir only
+      code-review:
+        workspace_access: true            # gets both scoped dir + workspace
+```
+
+When `workspace_access` is enabled, the runner passes both paths in the
+plugin's invocation JSON:
+
+```json
+{
+  "scope_dir": "$LOOM_HOME/agents/researcher/plugins/code-review/",
+  "workspace_dir": "/path/to/project"
+}
+```
+
+The plugin decides how to use each. A code-review plugin might read project
+files from the workspace while storing its review state in its scoped
+directory. The separation still holds — the scoped directory is the plugin's
+private state, the workspace is shared read-write access to the project.
+
+Without `workspace_access`, the plugin only receives `scope_dir`. This is
+the safe default: most plugins (memory, caching, scheduling) don't need to
+see project files.
+
+This separation means:
+- **Workspace** = the agent's view of the outside world (project files, data)
+- **Plugin scoped directories** = the plugin's private internal state
+- **Workspace access** = opt-in grant for plugins that need to operate on project files
+
+### Bash sandboxing
+
+Bash is the most powerful tool and the hardest to sandbox. A shell command can
+access the network, spawn processes, and read files outside the workspace via
+subprocesses.
+
+loom takes the pragmatic approach: **bash is opt-in, and the operator assumes
+responsibility**. When enabled:
+
+- The command runs with `cwd` set to the workspace
+- The agent's `env` is applied
+- No network or process restrictions are enforced by the runner
+
+This matches how coding agents work today — bash is available, powerful, and
+trusted. Operators who need stronger isolation can run agents in containers
+or use OS-level sandboxing (namespaces, seccomp, etc.). A future ADR may
+define a restricted bash mode with network and filesystem constraints.
+
+## Consequences
+
+### Good
+
+**Fast tool execution.** Built-in tools run in-process with no subprocess
+overhead. A read-edit-grep cycle that would require three process spawns as
+plugins executes in microseconds.
+
+**Familiar tool set.** Developers and LLMs both know these tools. The same
+read/edit/grep/glob/bash pattern used by coding agents works here. No new
+abstractions to learn.
+
+**Safe by default.** Workspace sandboxing means an agent can't accidentally
+(or intentionally) modify files outside its designated area. Operators
+explicitly choose what the agent can access.
+
+**Clean separation.** Workspace for project files, plugin directories for
+internal state. Neither can see the other. This prevents an agent from
+accidentally overwriting its own memory files via `edit`, or reading its raw
+inbox messages.
+
+### Tricky
+
+**Bash escapes the sandbox.** A `bash` command can `curl`, write to `/tmp`,
+or read outside the workspace. This is accepted — bash is opt-in and operators
+take responsibility. Stronger sandboxing is an OS-level concern.
+
+**Workspace override requires trust.** When an operator sets
+`--workspace /path/to/my-project`, the agent gets read-write access to that
+entire directory tree. This is powerful and necessary, but the operator must
+understand the implications.
+
+**Tool configuration is per-agent.** Operators can disable any built-in tool,
+which means different agents in the same weave may have different tool sets.
+This is intentional — a read-only research agent shouldn't have write/edit,
+while a coding agent needs everything. The runner resolves the tool list at
+startup and it's fixed for the agent's lifetime.
+
+**Plugin directory proliferation.** Each plugin gets its own directory under
+`plugins/`. Many plugins means many subdirectories, but they are contained
+under a single parent — `ls agents/{name}/plugins/` shows the full layout.
+
+## Alternatives considered
+
+**All tools as plugins (subprocess spawn):**
+Consistent with ADR-005, but unacceptably slow for tools called on every LLM
+turn. A read-edit-grep cycle would spawn three processes. Rejected.
+
+**No workspace sandboxing (full filesystem access):**
+Simpler implementation, but a managed background agent with write access to
+`/` is a liability. The default should be safe. Rejected for default behavior;
+available via `--workspace /`.
+
+**Restricted bash via seccomp/namespaces:**
+The runner could enforce network and filesystem restrictions on bash commands
+using OS primitives. Feasible but complex, platform-specific, and out of scope
+for v1. Deferred to a future ADR.
+
+**Capability-based tool permissions (mandatory declarations):**
+Each agent must explicitly declare which tools it needs. Rejected — too much
+friction for the common case. The opt-out model (everything on by default,
+disable what you don't want) is simpler and covers the same use cases.
+
+## References
+
+- ADR-001: Unix process model — agents have `cwd` and `env`
+- ADR-002: Filesystem as process table — agent directory layout
+- ADR-005: Runner architecture — tool execution protocol and plugin spawning
+- ADR-006: CLI and lifecycle — `loom run` modes and workspace defaults