Split sessions.rs, and make the agent event contract a type

[ParallelEntrepreneur]

Ported onto main

This branch was written before the publish stages (#122), the pull-request watcher, the spend budget and the host-disk quota landed, and it still carried eight commits that had already been squashed onto main — which is why it showed 73 changed files and could not be merged. The branch has been rewritten: the work is redone against main as it stands, in one commit. Its CI half is already on main as #138, so what is left here is the refactor and the typed contract.

The split

sessions.rs was 2,963 lines. What moved out, by what it does:

Module	Holds
events.rs	The live agent link: one websocket per colony, the event stream, memory proposals, findings, the autopilot decision
lifecycle.rs	Everything that ends or restarts a microVM — stop, cleanup, delete, resume, recovery, the sandbox tick — and the host's own limits (spend budget, host-disk quota), because passing one ends a colony the way the max session length does
publish.rs	Publishing the work, and watching the pull request afterwards
queue.rs	The parallel limit: who gets a slot, who waits, who starts next

sessions.rs keeps the types and the state they hang off: Session, Runtime, App's session methods, creating and booting a colony, and the browser-facing reads.

Tests moved with the code they cover. The shared fixtures stay in sessions::tests, and the modules that moved out use them. Behaviour is unchanged: the same 234 tests pass, plus six new ones below.

The agent events are a type now

protocol.rs replaces string matching over serde_json::Value in the dispatch:

• docs/agent-events.schema.json is the machine-readable contract for all thirteen event types; docs/protocol.md §2 stays the prose.
• The harness acts on seven. The rest, and any type a newer runner adds, land on AgentEvent::Other, so a new event type can never make a line fail to parse. Every line still reaches the browser before dispatch.
• A line whose type this build acts on but whose body it cannot read is now logged on the colony rather than silently doing nothing.
• modules/agents/claude-code/test/fixtures/events.jsonl is the runner's real output, and both sides test against it: the runner's suite validates it against the schema, and the harness deserialises every line into the variant the dispatch expects. Drift fails a test on both sides.

Verification

• cargo test --workspace: 240 passed (234 before the split, plus six contract tests).
• cargo clippy --workspace --all-targets -- -D warnings: clean.
• npm test in modules/agents/claude-code: 59 passed.
• npx tsc --noEmit and npx vitest run in web: clean, 67 passed.

Refs #73

[ParallelEntrepreneur]

Split, not superseded — #138 takes the half of this that lands clean on current main, and this PR should keep the other half.

In #138: the CI workflow and PR template, agentd's no-KVM smoke test, the runner's event fixtures and extra fake-sdk tests, and the web UI's 65 tests. Plus the sixteen clippy findings on main that the new -D warnings gate would otherwise have gone red on immediately — thirteen nested ifs that are let-chains, an iter().any() that is contains, a while-let that is a for loop, and a function after mod tests. One of those, the ci.yml comment pointing at crates/colonizer/src/boot.rs:66, was repointed at where the credential gate lives without the refactor.

Left here: the sessions.rs split into boot.rs, events.rs, lifecycle.rs, protocol.rs, publish.rs and queue.rs, with docs/agent-events.schema.json.

That part needs a real rebase rather than a mechanical one. It moves about 1,400 lines that main has changed since this branch was cut: the update sweep and Session.app_slot (#112), publish_stage (#87), the accepts_commands fix so an answer cannot be dropped silently (#114), and mem0 (#97). A cherry-pick resolves those as "ours deleted / theirs modified" — the danger is that a moved copy silently reverts a fix instead of failing to compile, so it should be redone by whoever made the split, function by function, against main.

Once #138 lands, that rebase gets checked by CI on its own pull request, which is the point of doing it in this order.