chore: convert flows, deprecate box2d raw slots, drop legacy renderEventEntry (RFC-PLUGIN-EVENTS phase 6)

[apotema]

Phase 6 of RFC-PLUGIN-EVENTS. Tracker: flow-codegen#11.

Scope

Cross-repo cleanup once phases 1-5 are stable: convert every in-tree flow to the new form, deprecate then remove labelle-box2d's raw callback slots, and delete flow-codegen's legacy OnEvent codegen.

1. Convert in-tree flows. Run the phase-3 legacy_onevent_to_name converter on every .flow.jsonc in the toolkit — bouncing-ball, flying-platform-labelle, bakery-game (and any other shipped game with OnEvent flows). Commit per-repo.
2. labelle-box2d deprecation. Mark the pub var on_collision_begin / on_collision_end / on_collision_hit / on_sensor_enter / on_sensor_exit slots (labelle-box2d/src/root.zig:90-95) deprecated. After a deprecation window (one release), remove them entirely and drop the raw-slot calls from processContacts / processSensorEvents (they become game.emit-only — the dual-emit code added in phase 2 becomes the only emit).
3. flow-codegen legacy deletion. Drop the v1 renderEventEntry legacy path (codegen.zig:517-575 — the setup() + flowEvent + slot-assign codegen). Remove the legacy module/callback/params fields from flow_io.Event.OnEvent. Update / delete tests pinning the legacy form.

This is cross-repo. The legacy renderEventEntry deletion is the most concrete artifact; the box2d deprecation can be split into its own follow-up sub-ticket if a longer deprecation window is wanted.

Success criteria

• No .flow.jsonc in the toolkit uses the legacy module+callback+params form.
• labelle-box2d exposes only pub const Events — the pub var on_collision_* slots are gone.
• flow-codegen's renderEventEntry is single-path (new-form only); the legacy code-path is deleted; the test suite is green.

Blocked on

• All of: feat: discover plugin Events and merge into AllHookPayloads (RFC-PLUGIN-EVENTS phase 1) labelle-assembler#174 (phase 1), labelle-toolkit/labelle-box2d (phase 2), labelle-toolkit/flow-codegen (phase 3), labelle-toolkit/labelle-assembler (phase 4), labelle-toolkit/labelle-gui (phase 5) — shipped and stable.

References

• RFC: Migration, Phased plan §6.

[apotema]

Phase 6 landed across two repos

flow-codegen 1b5e460 (main)

Retire the v1 OnEvent form end-to-end:

• flow_io.Event.OnEvent drops module / callback / params; name becomes non-optional. Phase 7's priority: ?i32 is preserved as the only sibling decl.
• buildEvent rejects an OnEvent carrying any retired key as MalformedFlow; a missing name is also MalformedFlow. The two-form structural-completeness check is gone.
• writeEvent emits the new shape verbatim: { "type": "OnEvent", "name": ..., "priority": ... }.
• legacy_onevent_to_name + ConvertError + the cloneParams/Nodes/NodeKind/Edges helpers are deleted. optStr (its only caller) and eventHasParam (the legacy OnEvent.params validator) follow them out.
• codegen.zig renderEventEntry collapses to a one-line tail call into renderNewFormEventEntry. The v1 flowEvent + pub fn setup + raw-slot-assign codegen is gone.
• CodegenError.UnsupportedNodeKind and CodegenError.EntityUnavailableInSubgraph are removed (only raised by the legacy branch). DanglingPin (the RFC §9 per-node check) is the surviving entity-scope diagnostic.
• anyNodeNeedsEntity orphan helper deleted.
• build.zig: the convert step is removed; tools/convert_legacy_onevent.zig is deleted.
• Tests: 9 legacy tests (parser, round-trip, both-set / neither-set / partial-legacy rejections, the converter suite, the legacy codegen tests) deleted; 3 retired-key rejection tests added (module / callback / params). Phase-7's 7 priority tests stay green (one assertion updated for the non-optional name). 89 of 89 pass.

labelle-box2d bb80ab9 (main)

Soft deprecation of pub var on_collision_* / on_sensor_* (src/root.zig:138-143). The dual-emit game.emit(.{ .box2d__... = ... }) lines stay paired with the legacy slot guards for one more release; the comment block above the slots flags them deprecated and notes the next-release removal plan. I picked soft over hard because hand-written games not in this monorepo may still assign these slots; pulling the legs out from under them in the same release as the converter deletion is the kind of break that deserves its own follow-up issue rather than riding on this cleanup.

Verification

• flow-codegen: zig build + zig build test green (89 tests, down from 98 — the deleted nine).
• labelle-box2d: zig build + zig build test green.
• bouncing-ball (canonical post-conversion target, hit_counter.flow.jsonc on the new form): rm -rf .labelle scripts/flows/*.zig; labelle-assembler generate --project-root .; cd .labelle/raylib_desktop && zig build — green.
• labelle-assembler/examples/flows-smoke (lifecycle OnCreate flow): same regeneration cycle — green.
• flying-platform-labelle ships no .flow.jsonc (no flow consumers); bakery-game doesn't exist in the monorepo.

Out of scope (no in-tree legacy flows to convert)

Task 1 was already complete on arrival — bouncing-ball/scripts/flows/hit_counter.flow.jsonc was converted in 8a3b4c5 and no other .flow.jsonc in the toolkit used the legacy module+callback form. The repo scan came up empty (find labelle-toolkit -name "*.flow.jsonc" -not -path "*/wt-*" -exec grep -l '"module"\|"callback"' {} \;).

Follow-up

A separate hard-removal release ticket against labelle-box2d should delete the pub var on_collision_* / on_sensor_* lines and the matching if (cb) |…| cb(...); call sites in processContacts / processSensorEvents once the deprecation window closes.