Specify and plan M3b: the runner and the tools

A draft spec for the owner's review and 13 offline tasks with their given
tests: shared tool arguments and host rules in proto, the sealed fetch
target (M3a finding 14), the toolkit tools and SOCKS5 egress proxy, and
brokerd's [runner], podman argument lists, runtime and proxy lifecycle. Each
task's tests were run against a reference at that task's end state (560 to
638 tests, clippy clean); the reference is not in the repository. Adds the
runner-unavailable runbook entry and tip T23 (ETXTBSY in script tests).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/plans/M3b/files/crates/brokerd/tests/fixtures/podman/egress.args

@@ -0,0 +1,20 @@
+run
+-d
+--rm
+--name=boxmaker-s1-1-7-egress
+--label=boxmaker=egress
+--network=pasta
+--read-only
+--cap-drop=all
+--security-opt=no-new-privileges
+--userns=keep-id
+--pids-limit=64
+--memory=128m
+--volume=/h/run/egress/boxmaker-s1-1-7:/run/egress:rw
+localhost/boxmaker-tools@sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+/bin/toolkit
+egress-proxy
+--socket
+/run/egress/egress.sock
+--allow
+example.com,*.example.org

docs/plans/M3b/files/crates/brokerd/tests/fixtures/podman/http_fetch.args

@@ -0,0 +1,17 @@
+run
+--rm
+-i
+--name=boxmaker-s1-1-7
+--label=boxmaker=tool
+--network=none
+--read-only
+--cap-drop=all
+--security-opt=no-new-privileges
+--userns=keep-id
+--pids-limit=128
+--memory=512m
+--tmpfs=/tmp:rw,size=64m,mode=1777
+--volume=/h/run/egress/boxmaker-s1-1-7:/run/egress:rw
+localhost/boxmaker-tools@sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+/bin/toolkit
+http_fetch

docs/plans/M3b/files/crates/brokerd/tests/fixtures/podman/read_file.args

@@ -0,0 +1,17 @@
+run
+--rm
+-i
+--name=boxmaker-s1-1-7
+--label=boxmaker=tool
+--network=none
+--read-only
+--cap-drop=all
+--security-opt=no-new-privileges
+--userns=keep-id
+--pids-limit=128
+--memory=512m
+--tmpfs=/tmp:rw,size=64m,mode=1777
+--volume=/home/kyle/notes:/home/kyle/notes:ro
+localhost/boxmaker-tools@sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+/bin/toolkit
+read_file

docs/plans/M3b/files/crates/brokerd/tests/fixtures/podman/shell.args

@@ -0,0 +1,18 @@
+run
+--rm
+-i
+--name=boxmaker-s1-1-7
+--label=boxmaker=tool
+--network=none
+--read-only
+--cap-drop=all
+--security-opt=no-new-privileges
+--userns=keep-id
+--pids-limit=128
+--memory=512m
+--tmpfs=/tmp:rw,size=64m,mode=1777
+--volume=/srv/a:/srv/a:rw
+--volume=/srv/b:/srv/b:rw
+localhost/boxmaker-tools@sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+/bin/toolkit
+shell

docs/plans/M3b/files/crates/brokerd/tests/fixtures/podman/shell_no_paths.args

@@ -0,0 +1,16 @@
+run
+--rm
+-i
+--name=boxmaker-s1-1-7
+--label=boxmaker=tool
+--network=none
+--read-only
+--cap-drop=all
+--security-opt=no-new-privileges
+--userns=keep-id
+--pids-limit=128
+--memory=512m
+--tmpfs=/tmp:rw,size=64m,mode=1777
+localhost/boxmaker-tools@sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+/bin/toolkit
+shell

docs/plans/M3b/files/crates/brokerd/tests/fixtures/podman/write_file.args

@@ -0,0 +1,17 @@
+run
+--rm
+-i
+--name=boxmaker-s1-1-7
+--label=boxmaker=tool
+--network=none
+--read-only
+--cap-drop=all
+--security-opt=no-new-privileges
+--userns=keep-id
+--pids-limit=128
+--memory=512m
+--tmpfs=/tmp:rw,size=64m,mode=1777
+--volume=/home/kyle/out:/home/kyle/out:rw
+localhost/boxmaker-tools@sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+/bin/toolkit
+write_file