render: document createSurface as an explicit no-op in Apply

[joestump]

What

Apply (render/composite.go) silently dropped createSurface messages. This PR makes the stance explicit and documented rather than implicit: a2tea deliberately ignores createSurface — a surface is established by its first updateComponents, host WithStyles owns theming, and the component catalog is compiled in.

How

• Apply gains an explicit case m.CreateSurface != nil no-op with a doc comment, and the Apply doc comment spells out the rationale: the message's theme hints (primaryColor, iconUrl, agentDisplayName) have no honorable mapping in a deliberately monochrome renderer where the host theme wins, and catalogId is ignored because the catalog is compiled in, by design. (Inspected tmc/a2ui's CreateSurface/Theme to confirm nothing is trivially honorable — applying primaryColor would violate the monochrome-chrome contract.)
• docs/wire-format.md moves createSurface from the Not yet list to a documented decision in the implemented section.

Tests

• TestApplyCreateSurfaceIsNoOp: a createSurface (with catalog URI + theme) neither errors nor mutates state — rendered view is byte-identical before/after, theme text does not leak, the surface stays alive, and focus survives (Enter still activates the focused button).
• TestApplyCreateSurfaceDoesNotCreateState: createSurface alone does not make a surface renderable; the createSurface → updateComponents batch shape agents actually send establishes it via the updateComponents.
• Gate: go build ./... && go vet ./... && go test ./... all green locally.

Note: the ticket's Done-when also mentions the site's "Not yet"/implemented lists — website/ changes are deferred to the post-merge docs pass per repo policy.

Fixes #47

🤖 Posted on behalf of @joestump by Claude.

[joestump]

Adversarial review of the createSurface no-op change (issue #47). Verdict: no blockers; two nits.

What I verified

• Gate: go build ./... && go vet ./... && go test ./... all green on the branch; both new tests pass with -count=1 (not cache artifacts).
• State preservation: the no-op case in render/composite.go:38 cannot mutate anything — confirmed by reading Apply/applyComponents; TestApplyCreateSurfaceIsNoOp asserts real behavior (byte-identical View().Content, theme text does not leak, focus survives and Enter still emits ButtonClicked{ID: "btn2"}), not mere execution.
• Alive semantics: TestApplyCreateSurfaceDoesNotCreateState correctly pins that createSurface alone leaves rootID == "" (Apply returns false) and that the realistic createSurface → updateComponents batch establishes the surface. Matches Render's first-updateComponents establishment in a2tea.go:130-141.
• Ticket Done-when: explicit case + doc comment in code ✅, docs/wire-format.md moved from "Not yet" to a documented decision ✅, tests ✅, website/ untouched and the deferral is called out in the PR body per repo policy ✅.
• Type claims: checked tmc/a2ui v09 — Theme really is primaryColor/iconUrl/agentDisplayName, and nothing on CreateSurface maps onto the monochrome-chrome contract. The rationale in the doc comment is accurate.

Nits (non-blocking)

1. sendDataModel is ignored but undocumented — render/composite.go:21-26 and docs/wire-format.md enumerate theme and catalogId as the ignored payload, but a2ui.CreateSurface carries a fourth field, SendDataModel bool (v09/message.go:24), which this no-op also drops. Since the whole point of #47 is "no silent drops," add one line noting sendDataModel is likewise ignored (a2tea has no client→agent data-model channel; ActionEvent.Context already round-trips input values). Fine to fold into the post-merge docs pass.
2. Switch-order shadowing on malformed messages — the new case m.CreateSurface != nil at render/composite.go:38 precedes UpdateComponents, so a spec-invalid message carrying both createSurface and updateComponents now drops the components where it previously applied them. The wire format is a one-of, and Scan validates upstream, so this is theoretical — but placing the no-op case last would make Apply strictly more forgiving at zero cost.

🤖 Posted on behalf of @joestump by Claude.