---
kind: guide
status: active
---

# Whole mutator-class lease gate

> **Status:** Current contract reference.
> **Audience:** Developer and security reviewer.
> **Evidence:** Runtime launch-guard and mutator-gate tests cross-check this boundary; parser residuals and deployment gaps remain explicitly labeled below.

WI-2 adds the framework-native authorization boundary for Claude (including the supported Claudex overlay) and Pi. Every runtime-reported tool name reaches the lease broker before execution. The gate classifies capabilities by the whole tool class; it never parses a Bash command to decide whether that particular string looks read-only.

## Default-deny policy

While a session is not VERIFIED, only these exact classes are allowed:

- Claude: `Read`, `Grep`, `Glob`, `Ls`, `Find`
- Pi: `read`, `grep`, `find`, `ls`
- Both runtimes: the fixed `mosaic_context_recover` primitive

Every other built-in, unknown tool, and custom/MCP tool is consequential by default and is denied. This includes Claude `Bash`, `Edit`, `Write`, and `NotebookEdit`, plus Pi `bash`, `edit`, and `write`. A compromised model therefore cannot bypass Mosaic wrappers by selecting raw `git`, `curl`, `kubectl`, provider, deployment, or filesystem commands inside a generic mutator—the generic mutator itself is blocked before its input executes.

## Broker-owned transition order

The authenticated broker is the sole lease writer:

1. `begin_verification` revokes existing authority and pending tokens first, then records `PENDING_VERIFICATION` and mints one WI-1 single-use promotion token bound to the exact cycle.
2. `promote_lease` accepts only that session/generation/binding/token combination.
3. Token consumption commits before the volatile lease becomes VERIFIED. Promotion is last and cannot be reached directly from UNVERIFIED.
4. `revoke_lease`, a runtime-generation increase, broker restart, or monotonic expiry removes mutator authority.

The initial TTL is capped at the ratified 300-second maximum. A caller may request a shorter positive TTL but cannot lengthen the maximum. WI-3 installs the [compaction observer and generation lifecycle](compaction-revocation.md). Dual compaction-hook miss within an unexpired lease remains the ratified bounded T-A residual: consequential tools are allowed until expiry, with no claimed within-window action bound; once either observer revokes or TTL expires, the next consequential tool is denied.

A receipt is only a future promotion prerequisite. It is not an obedience, residency, or safety proof and never replaces this mechanical gate.

## Runtime adapters

`launch-runtime.py` registers itself with the broker and then `exec`s Claude or Pi so PID/starttime remain the authenticated parent anchor. It exports the broker-minted session ID and an owner-only generation-file reference to descendants; lifecycle hooks advance that file for same-PID replacement generations.

- Claude installs `mutator-gate.py` as an all-tools (`.*`) `PreToolUse` hook.
- `mosaic claudex` and `mosaic yolo claudex` preserve their isolated `CLAUDE_CONFIG_DIR`, merge the mandatory hook into that isolated `settings.json`, and use the same register-before-exec launcher. Malformed or symlinked isolated settings deny launch.
- Pi invokes the same executable from its `tool_call` handler.

The executable submits the runtime's actual tool name to `authorize_tool`. Missing identity, malformed input/reply, timeout, broker unavailability, or denial exits with status 2 and blocks fail-closed.

## Runtime-launch choke-point and permanent guard

Every repository-owned Claude/Pi launch entry converges on `launch-runtime.py`, either directly or through `mosaic` → `execLeaseGatedRuntime`. PRDY init/update and QA remediation invoke the wrapper directly so their existing prompts, dangerous-permission behavior, working directory, and environment survive without skipping broker registration. The raw Claude `--dangerously-skip-permissions` primitive is owned only by `launch-runtime.py`; callers request semantic `--dangerous` mode, and the wrapper validates Claude before injecting the primitive. `@mosaicstack/coord` rewrites direct Claude commands to `mosaic claude` and rejects unknown custom Claude launchers.

`check-runtime-launches.py` is the permanent completeness guard. It scans production shell, TypeScript/JavaScript, Python, and data launch definitions under `packages/`, `apps/`, `plugins/`, and `tools/`; direct literal, absolute-path, process-API, dynamic, command-substitution, `eval`, and variable-execution runtime launches fail. Shell comments are stripped with quote awareness, wrapper prefixes are tokenized with `shlex`, and only an invocation in command position with `--runtime` before the command separator is gated. Literal and tracked-variable command tokens use one terminal resolver after any nesting of `exec`, `command`, `nohup`, or `env` plus assignments. A direct command always wins over an inert marker on the same line. Independently, the raw dangerous primitive anywhere outside the choke-point is RED.

The command parser is a best-effort CI defense, not a complete shell interpreter. Alias/function redefinition, sourced commands, generated scripts, and encoded pipelines are intentionally residual rather than an invitation to chase an unbounded shell language. Two runtime controls backstop that residual surface: primitive ownership rejects a dangerous launch even when command identity is alias-indirected, and Claude's global `.*` `PreToolUse` hook invokes the broker gate for non-dangerous launches. Without `MOSAIC_LEASE_SESSION_ID`, representative read, mutator, and custom/MCP tools all fail closed with `GATE_UNAVAILABLE`. Hook absence or replacement remains in the documented T-C boundary.

### Parser stopping criterion

- **A — realistic parser matrix:** comments, inert strings/assignments, heredocs, continuations, chained commands, command substitution, `eval`, bare tracked variables, and quoted/unquoted tracked variables behind `exec`, `command`, `nohup`, or `env` are permanent RED regressions. Prefix-variable forms are covered in both multiline and same-line assignment shapes.
- **B — residual backstops:** a dangerous alias-indirected launch is RED solely through primitive anchoring; a parser-missed non-dangerous alias launch is paired with an acceptance test proving the global all-tools hook denies every representative tool class as `GATE_UNAVAILABLE` without a lease.
- **C — independent fresh review:** the parser class is considered complete only when reviewers find no new non-overlapping realistic evasion on the exact head. A and B are repository evidence; C is supplied by the fresh review round.

All three layers are load-bearing and complementary. The guard is mandatory in `@mosaicstack/mosaic`'s test script, so root CI fails on a future realistic bypass. Real-socket tests separately prove PRDY init/update and QA receive broker sessions and deny an unverified mutator.

The live inventory is emitted by:

```bash
python3 packages/mosaic/framework/tools/lease-broker/check-runtime-launches.py --root . --json
```

| Production launch family                               | Gated entries |
| ------------------------------------------------------ | ------------: |
| `@mosaicstack/coord` default/configured Claude command |             2 |
| Fleet runtime start                                    |             1 |
| QA remediation + generated QA command                  |             2 |
| Orchestrator command construction/session launches     |             3 |
| PRDY init/update                                       |             2 |
| Mosaic Claude/Pi/Claudex adapter and wrapper boundary  |             4 |
| **Total**                                              |   **14 / 14** |

## Assurance boundary

This closes T-A after an observer fires or lease expiry and T-B for in-runtime tool calls. Hook/extension absence, a runtime executing outside the gated launcher, ptrace/same-UID broker replacement, and other fully rotted behavior remain T-C. Server-side branch protection and required PR review/CI remain the irreducible line for protected repository mutations.
