Deadlatch

The pre-trade latch for your trading agent. Advisory-only.

Three things you need to know before anything else:

1. You need an independent, cross-broker gate that you control. If an agent can place orders on your account, the last check between the agent and the broker should not be the agent itself — and it should not be locked to one broker's UI or rules.
2. Deadlatch does not predict, does not recommend, and does not place orders. It answers one question only: is this order allowed right now? It is not a signal generator and it is not a broker.
3. Every answer comes with reasons, evidence, and a local audit record on Linux/macOS. PASS / WARN / BLOCK is never a bare verdict — you can see which rule hit, why, and what was evaluated. Durable audit writes (init / append / repair / prune / shadow report) are supported on Linux and macOS only. On Windows the package still imports, and the rule engine / Guard / CLI / MCP still compute decisions; those write paths fail closed with audit_platform_unsupported. Offline verify / read of a stopped snapshot remain available. Windows MCP is a limited integration path, not a full trusted audit chain.

Honest boundary (please read): Deadlatch is advisory. It cannot force an agent that never calls it to call it, and it cannot stop an agent that ignores a BLOCK from submitting the order somewhere else. Whether the agent calls the guard and honors the result is the integrator's decision. Do not rely on this tool as a guarantee against loss — it is a gate, not an insurance policy.

• License: MIT — see LICENSE.
• 中文文档: README.zh-CN.md
• Security: SECURITY.md · Contributing: CONTRIBUTING.md · Disclaimer: DISCLAIMER.md

Start here

The current install path is the verified PyPI deadlatch==0.1.2, published on 2026-09-22. The stable GitHub v0.1.2 Release targets b072e8a4d4b053e1d5a428dbb9c47e06652fbf4c; its wheel/sdist assets match the PyPI originals.

pip install deadlatch==0.1.2

The published MCP Registry name is io.github.Diabloluo/deadlatch at version 0.1.2, verified active/latest on 2026-09-22. The local server.json matches that published version. The command below starts the verified PyPI package directly.

MCP-first start:

uvx --from deadlatch==0.1.2 deadlatch-mcp --policy policy.yaml --portfolio portfolio.json

--policy and --portfolio are required local files. --audit-path and --kill-switch-path are optional. Use fictional or your own simulated inputs only. Deadlatch is advisory-only: it never places orders and cannot stop an agent that never calls it. Option orders must use the broker's unique full contract code as symbol. A historical GitHub pre-release remains at v0.1.0.dev1; it is not the current install path.

Then:

1. Run a fictional-data Quick Start below (Python, CLI, or MCP) on Linux or macOS. Confirm PASS → BLOCK → local audit. Windows can import the package and run rule computation; it is not the audit-write Quick Start.
2. Request a 20-minute integration assessment only if you already have an order-intent or simulated execution path: open the assessment form.

That GitHub issue is public. Do not paste accounts, positions, orders, API keys, tokens, customer names, or private paths. Security defects must go through GitHub Security Advisories, not a public issue.

Quick Start (60 seconds each)

All three quick starts use fictional data and a temporary audit path. They are executed from the same source scripts by the test suite, so they cannot drift from the documentation. Full audit-write / MCP Quick Start requires Linux or macOS. Windows may import the library and evaluate rules; it will not initialize or append a durable audit collection.

1. Python API

pip install dist/deadlatch-*.whl        # or: pip install -e .
python docs/quickstart/python.py

Shows Guard.from_policy(...) → Order / Portfolio → guard.check(...): a valid order returns PASS / 0; an oversized order returns BLOCK / 3 with the hit rules; on BLOCK the example caller stops — no broker call is ever made.

2. CLI

bash docs/quickstart/cli.sh                  # requires `deadlatch` on PATH

Creates fresh inputs in a temp directory (dynamic timestamps — never goes stale), then runs deadlatch check for PASS (exit 0), BLOCK (exit 3), an input error (exit 4), and a --json check, plus shadow report --json over the audit.

3. MCP (stdio)

python docs/quickstart/mcp_client.py         # requires `deadlatch` installed

Starts deadlatch-mcp as a real subprocess over stdio, lists the five tools, and calls check_order once for PASS and once for BLOCK. policy / portfolio / audit paths are server startup configuration — an agent cannot swap them as tool arguments. BLOCK is a constraint the caller must honor; technically the guard cannot force a fully bypassing agent to call it.

What it is / is not

Who should use it

• Teams that already have an order-intent or simulated execution path and want an independent, deterministic pre-trade gate with a local audit trail.
• Developers who want a small, dependency-light, fail-closed building block they can integrate into their own execution pipeline.
• Anyone who wants to evaluate orders against a policy they control, expressed as plain YAML.

Who should not use it: anyone expecting a profit guarantee, a backtest engine, a portfolio manager, or a tool that enforces itself. If the agent never calls the guard, or ignores a BLOCK, nothing in this repository can stop it.

Core security boundary

• Local: everything runs on your machine; no account credentials are ever stored, read, or transmitted.
• No network core path: the library, CLI, and MCP server never open a socket, never register an HTTP/SSE route, and never call out for quotes or anything else (the MCP SDK's HTTP stack is a transitive dependency that business code never imports).
• Never places orders: the core package (library, CLI, MCP server) has no broker connectivity and never submits orders. Experimental read-only mapping examples exist only in the development workspace; they are not included in the public candidate or the wheel, and they are not live-verified integrations.
• Fail-closed: missing or malformed data → BLOCK (exit 3); input/config errors → exit 4; internal errors → exit 5. An uncertain state is never reported as PASS.
• Direction is snapshot-derived: order-side text is never accepted as proof of a close. Stock and option closing intent is recognized only when a fresh portfolio snapshot contains a matching, opposite-side position with sufficient quantity. For options, symbol must be the broker's unique full contract code; never reuse an underlying ticker across different expiries, strikes, or rights.
• USD-only (v0.1): any currency mismatch (order, portfolio, positions) is an input error (exit 4); the MCP account-status tool fail-closes on mismatch.

Write surface: the tool never modifies policy, portfolio, or kill-switch state, never connects to a broker, and never places an order. Two kinds of intentional local file writes exist:

1. Audit subsystem: Guard.check() / check_order append one sanitized v2 record to a UTC day shard next to the logical audit path (30-day retention). Append is a bounded tail write under a shared lock; it does not rewrite history. A new collection needs one explicit deadlatch audit init (or initialize_audit_state) before append; Guard/MCP never auto-migrate. deadlatch shadow report and deadlatch audit prune delete whole shard files that fall outside the 30-calendar-day window. deadlatch audit repair --quarantine still uses lock/tmp files and os.replace when it isolates a truncated tail. Ordinary append is not crash-atomic across files. POSIX locks are cross-process. v0.1.2 durable audit writes are Linux/macOS only; Windows writers receive audit_platform_unsupported and do not skip directory fsync to report success.
2. Explicit migration output: deadlatch migrate --output <file> writes the migrated document only when you explicitly pass --output.

The public contract for these rules, Decimal thresholds, exit codes, and option-symbol requirements is docs/rules-spec.md.

The 12 rules (v0.1)

Optional rules (R3–R7) are toggled by their config keys in policy.yaml; a missing optional key must be declared in acknowledged_disabled or the policy is rejected (exit 4). Mandatory rules (R1, R2, R8–R12) can never be disabled.

Exit codes

In shadow mode the internal verdict is recorded (shadow_verdict) while the external projection is PASS / 0; kill-switch hits and exit 4/5 are never projected away.

Data contracts & migration

Schemas are versioned JSON Schema 2020-12 files shipped inside the package: order, portfolio, policy, result, audit-record, shadow-report, audit-maintenance-result, audit-prune-result, audit-write-state, audit-state-result. Explicit offline migration is available for legacy documents:

deadlatch migrate --kind order    --input order_v1.json    [--output out.json]
deadlatch migrate --kind policy   --input policy_v1.json   [--output out.json]
deadlatch migrate --kind portfolio --input portfolio_v1.json [--output out.json]

Migration converts only adjudicated fields (e.g. policy v1 boolean kill switch → off/full); it never guesses business fields. Normal evaluation entries reject old versions (exit 4) rather than silently migrating.

Audit log

Every Guard.check() appends one v2 record to a UTC day shard beside the logical path (default ~/.deadlatch/audit.jsonl, overridable via --audit-path / DEADLATCH_AUDIT_PATH). A new collection must be initialized once with deadlatch audit init / initialize_audit_state before append; missing state refuses the write and does not scan the directory to rebuild it. Pre-v0.1.2 single files remain readable as legacy v1. Records are schema-validated and sanitized (no credentials, cookies, or absolute paths in plaintext). Retention is 30 calendar days of shards; append no longer rewrites history. The UTC shard date is decided after the collection lock is held (default clock or explicit now). A durable write-date watermark (audit.jsonl.state.json) refuses any earlier UTC day after a later day has been reserved, including gaps of 30/365 days; original log and state bytes stay unchanged. The watermark is sequential control, not a signature. evaluated_at is not rewritten. Use deadlatch shadow report or deadlatch audit prune to delete expired shards. Legacy files are not auto-deleted. If the audit write fails, the returned result is degraded severity-only-up: PASS/0 → WARN/2; BLOCK/3/4/5 keeps its decision and just attaches an audit_write_failed warning — the disk and the returned Result never contradict each other. See docs/audit-write-state.md.

v0.1.2 records carry a local SHA-256 hash chain (prev_hash / record_hash). The chain is tamper-evident, not a digital signature and not tamper-proof. An attacker who can rewrite the whole directory and recompute hashes is out of scope. Without an external immutable anchor, deleting the current last record or the whole visible set is not reliably detectable from the chain alone.

deadlatch audit verify scans the visible collection (legacy plus UTC shards in the 30-calendar-day window and any future shards prune keeps) without changing contents or writing quarantine. Expired shards may remain unpruned and are not part of that chain check. For an existing collection it may create a .lock sidecar so it can share the same lock as append/repair/prune. Damaged legacy v1 lines can still be isolated with deadlatch audit repair --quarantine. v2 repair only isolates a truncated last line of the last shard; hash mismatches, duplicate IDs, version downgrades, and mid-chain damage refuse automatic relink (exit 3, no writes). Shadow report and MCP recent_decisions read the same snapshot under the same lock and verify hashes, chain links, duplicate IDs, and version location before returning records; a tampered or downgraded chain is not presented as trusted history. v1 compatibility is limited to the legacy baseline file and only before any v2 record — a v1 line in a UTC day shard is refused. See docs/postmortem-option-direction.md for a fictional explanation of the G1 option-direction fix.

MCP server

deadlatch-mcp is a stdio-only MCP server (no TCP listener, no HTTP/SSE routes). The five tools are read-only: none of them can modify policy, portfolio, or kill-switch state (those paths are startup configuration, not tool arguments). Policy changes are validated and loaded automatically on the next tool call. An optional independent kill-switch file is read on every call and can only make the policy more restrictive. Note the server still appends each check_order evaluation to the local audit log — that is by design, not a tool capability. Five tools:

Start it with:

deadlatch-mcp --policy policy.yaml --portfolio portfolio.json \
  [--audit-path audit.jsonl] [--kill-switch-path kill-switch]

The path arguments are startup configuration only; their file contents remain live local state. A configured kill-switch file must contain exactly off, reduce_only, or full. It cannot weaken a stricter mode already present in the policy. A missing, malformed, or concurrently unstable live policy/switch fails closed: tool errors are isError=true + fail_closed, and configuration errors carry input_error=true + exit_code=4.

Demo

An agent calls check_order with an oversized order; the guard returns BLOCK / 3 with the hit rules; the agent stops instead of calling any broker tool. Generated from a real local MCP stdio run with fictional data (tools/make_demo_gif.py):

Known limitations (v0.1)

• Naked short-call upside risk is unlimited. v0.1 uses a strike-based exposure approximation and does not model that unlimited tail; do not treat it as a conservative bound for short calls.
• Short-sell cash outflow is modeled as 0 (documented simplification).
• No Greeks, IV, multi-leg strategies, or multi-currency books.
• Audit cross-process locking relies on POSIX fcntl; on non-POSIX platforms the lock degrades to a process-local lock (no cross-process guarantee).
• Durable audit writes in v0.1.2 are supported on Linux and macOS only. Windows and other platforms refuse init / append / repair / prune / shadow report with audit_platform_unsupported before creating locks or writing state. File and directory fsync failures on supported platforms stay fail-closed; they are not treated as “capability missing”. Offline verify/read of a stopped snapshot remains available. Concurrent Windows writers are out of scope.
• The guard cannot prevent complete bypass: an agent that never calls it, or that ignores a BLOCK and calls the broker directly, cannot be stopped by this tool.
• Examples in the repository use fictional tickers and data only.

Governance

• SECURITY.md — supported versions, vulnerability scope, reporting.
• docs/rules-spec.md — public 12-rule contract.
• CONTRIBUTING.md — environment, test/schema/scan/coverage commands, rule discipline.
• DISCLAIMER.md — full legal/risk disclaimer (summary below).
• README.zh-CN.md — 中文文档.

Disclaimer (summary): not investment advice; no guarantee against losses; verify inputs and rules yourself; the guard never places orders; all examples are fictional; test before trading real capital; no SLA. See DISCLAIMER.md in full.