boxmaker/docs/plans/M3b

M3b implementation plan: the runner and the tools

For the implementing model: do not work from this file. The owner gives you one task file at a time (01-… to 13-…). This file is the index for the owner and the reviewer.

Goal: an allowed tool call runs in a fresh rootless Podman container, with no network unless it is http_fetch, which reaches the grant's hosts only through an egress proxy of our own. The four tools and the proxy are programs in toolkit; brokerd builds the podman argument lists and runs them.

Architecture: shared definitions move to proto first (01), the fetch target is sealed (02), and grant paths that cannot be mounted are refused (03). toolkit gets its four tools (04 to 06), the public-address check (07) and the proxy (08). brokerd gets [runner] (09), the argument lists (10), the runtime (11), the proxy's lifecycle (12) and the wiring in serve (13).

Spec: docs/specs/2026-09-22-m3b-runner.md. Brief: docs/design.md. Every fail-closed message ends with a pointer into docs/runbook.md; the runner-unavailable entry is already there.

No task needs Podman, Nix or a network. Everything runs against fakes: fake curl and podman scripts, a fake resolver, UnixStream::pair(). The image and the checks on straylight are done by the design model afterwards.

Global constraints

• Everything in AGENTS.md, including "Lessons from earlier reviews".
• No new dependency. toolkit gains serde and serde_json, both already vetted (task 04).
• Branch m3b. One task, one fresh OpenCode session, one commit. Run cargo fmt --all before the gate. Review happens once, after task 13.
• Tests that write a script and run it take a lock (serial()): otherwise another test's fork can make running it fail with "text file busy". Keep that pattern in anything you add.

Tasks

The last column is how the given tests were checked before hand-over (decision of 2026-09-18, tip T17). For M3b every task had a reference implementation: the tests of each task were run against it at that task's end state, then the reference was deleted so it cannot be read (tip T18).

#	File	Delivers	Tests	Check
01	01-proto-tools-hosts.md	proto::tools, proto::hosts; brokerd::args uses them	proto/tests/tools.rs, hosts.rs	reference; the given test pinned an accepted serde weakness, removed
02	02-brokerd-fetch-url.md	ToolArgs::HttpFetch(FetchUrl), sealed (M3a finding 14)	brokerd/tests/args.rs (changed), a compile_fail doctest	reference
03	03-brokerd-grant-mount-rule.md	grant paths with : or , are invalid	brokerd/tests/grants_mount.rs	reference
04	04-toolkit-files.md	the toolkit program, read_file, write_file	toolkit/tests/files.rs, support/mod.rs	reference
05	05-toolkit-shell.md	shell	toolkit/tests/shell.rs	reference
06	06-toolkit-fetch.md	http_fetch through curl	toolkit/tests/fetch.rs	reference; found the ETXTBSY race (1 in 7 runs), fixed with serial()
07	07-toolkit-addr.md	is_public	toolkit/tests/addr.rs	reference; found ::/96 missing from the spec, added
08	08-toolkit-egress-proxy.md	the SOCKS5 egress proxy	toolkit/tests/egress.rs	reference; 20 runs clean
09	09-brokerd-runner-config.md	[runner]	config_runner.rs, 5 fixtures, support/rig.rs (changed)	reference
10	10-brokerd-podman-args.md	the podman argument lists; RunSpec gains session and call	podman_args.rs, 6 golden files	reference
11	11-brokerd-container.md	the Podman runtime	container.rs, support/fake_podman.rs	reference; 20 runs clean
12	12-brokerd-egress.md	the proxy's lifecycle for http_fetch	container_egress.rs	reference; 20 runs clean
13	13-brokerd-serve-runner.md	brokerd serve uses the runtime	serve_runner.rs	reference

At the end: make gate prints gate: ok with about 638 tests.

Running it

BOXMAKER_MODEL=straylight/ornith-1.5-35b-a3b tools/run-plan.sh docs/plans/M3b

Keep the OpenCode TUI closed while it runs.