test(ws): cover PiP handling in macro CUT, TRANSITION, and TAKE

[wagenet]

Builds on #179 and #180. The diff contains all three commits until those merge — only the third, test(ws): cover PiP handling in macro CUT, TRANSITION, and TAKE, belongs to this PR.

Why

The macro PiP paths had no coverage, and neither does the WS controller as a whole — activation.test.ts and macros.test.ts both mock ../ws/controller.js out entirely. #179 and #180 rested on reading the interactive handlers and mirroring them, which is exactly the kind of change that deserves execution behind it.

What it does

Drives handleMessage with CouchDB and StromClient mocked, asserting the Strom call sequence and the broadcast payloads. PiP state is established through real inbound messages (SELECT_PVW_PIP, TAKE) rather than by reaching into the module-level maps, so each case exercises the same state machine the server runs in production.

Four cases:

Case	Asserts
macro CUT over a PGM PiP	PiP moves to preview, PIP_STATE emitted, selectPreview({pip:0}) called, from_input is the tracked background
macro TRANSITION over a PGM PiP	same displacement and restore
macro TAKE with a PiP in preview	Strom is called at all, PiP reaches program
macro CUT with no PiP	no PIP_STATE, no pip-addressed selectPreview, tally unchanged

It discriminates

A test that passes against broken code is worth nothing, so each case was run against the unfixed trees:

against main (neither fix)    3 fail, control passes
with #179 only                1 fails — the preview-PiP take
with both fixes               4 pass

The no-PiP control passes on all three, which is what makes it a control rather than a vacuous assertion. The single failure against #179 is precisely the bug #180 fixes.

Production change

One export:

/** Exported for tests: drives one inbound message against a production. */
export async function handleMessage(

handleMessage was module-private and the plugin only exposes a websocket route, so there was no seam. The alternative — a fastify + websocket fixture — would drive the connect handler too and test far more than these paths. If you would rather have that, I am happy to switch; this felt like the smaller commitment to make on your behalf. Nothing else in controller.ts moves.

Testing

• npx tsc --noEmit clean.
• npx vitest run — the new file passes 4/4. The suite's 27 pre-existing failures in activation.test.ts and macros.test.ts are unchanged (all 500s from the HTTP layer, present on main too).

Still not covered: anything requiring a real mixer. Strom builds and runs locally, but neither of its sample flows carries a vision mixer block and its own suite has no PiP coverage either, so selectPreview({pip:N}) setting pvw_pip such that the next transition takes the PiP to program remains supported by reading flows.rs and mixer_ops.rs rather than by execution.

[wagenet]

Absorbed into the stack. The harness is now #182 at the root, and each fix ships with the cases it makes pass — #179 carries the two displacement cases, #180 the preview-PiP take. That way every PR is green on arrival instead of two behaviour changes landing ahead of their tests.