[deferred] h3 unification decision point — blocked on h3 v2 stable (ADR-0123 item 11)

[SisyphusZheng]

Per ADR-0123 item 11: when h3 v2 reaches stable (currently 2.0.1-rc.26 per npm), evaluate rewriting the generated server app from Hono to h3 — dev/prod semantics unify, nitro-mount and the request-time parity gate retire. Constraints: the fetch middleware contract (ADR-0123 item 2) must make the swap invisible to users; Hono stays supported in user API routes; single-vendor consolidation on UnJS is an accepted trade-off to record in the deciding ADR amendment. Do not start before h3 v2 stable.

[SisyphusZheng]

Decision recorded (2026-08-02): NOT in alpha.13. Three reasons: (1) alpha.13 is the TP-6 freeze-prep train — the worst window to swap the server generator right before declaring the surface frozen; (2) h3 v2 being in the tree transitively via Nitro v3 shields us from rc API churn, but as a direct codegen target every rc break lands in user builds — h3 is at 2.0.1-rc.26, API not locked; (3) once the fetch middleware contract (#858) lands the swap is user-invisible, so it belongs in the lowest-risk window: first item of 0.43. Accepted compromise: an optional alpha.13 spike (branch-only h3 entry, run the full parity suite, report only, no merge) to give the 0.43 decision real data.

[SisyphusZheng]

Final decision (2026-08-02): postponed — do NOT schedule until h3 v2 ships a stable release. We evaluated the alternative sequencing (swap first in alpha.13, freeze after on the final form) and while it is architecturally cleaner, it fails the hard rule: no generated code on an RC base (h3 is 2.0.1-rc.26). alpha.13 proceeds with everything else: TP-6 freeze preparation, the six alpha.7 leftovers (#603-#606, #609, #610), and the standards train (#856-#860, #863-#867). When h3 v2 goes stable, this becomes the first item of the following train, ideally sequenced before the ADR-0122 acceptance so the freeze lands on the final form. Note for that train: user-side Hono (API routes) is unaffected by the swap — Hono apps are fetch handlers and mount on any base.