[Elizabeth Craig (ecraig12345)]

Stack

Stacked on #1262; merge that PR first, then retarget this PR to main. Uses #997 as a migration reference, without reverting the newer Node requirements or CI versions.

Summary

• Upgrade Fastify 4.29.1 → 5.12.7, coordinated Connect packages 1.7.0 → 2.3.0, and Protobuf runtime/generator 1.x → 2.16.0. Raise the Buf CLI range to ^1.75.0 and remove the obsolete Connect code generator.
• Regenerate Protobuf service descriptors, migrate createPromiseClient/PromiseClient to createClient/Client, and remove the obsolete httpVersion option (gRPC always uses HTTP/2).
• Adapt CLI task result typing to Protobuf 2's message initializer union without casts, update Node typings to the latest eligible 24.x (^24.19.2), and use native os.availableParallelism().
• Remove the obsolete Node 16 toad-cache resolution. Preserve unrelated dependency pins and all parent PR Node runtime/CI settings.
• Use Buf's STANDARD rules with narrowly scoped exceptions for existing proto paths/field names, preserving the wire schema. Update generated API reports and migration notes, and add Beachball entries.
• Add direct HTTP/2 integration coverage for ping, task payloads and output, present/absent optional fields, and Connect error propagation.

Release quarantine

These are the newest releases eligible under the unchanged eight-day quarantine as of 2026-11-07:

Dependency	Selected	Newer release still quarantined	Eligible at (UTC)
Fastify	5.12.7	5.12.8	2026-11-10 10:46:39.236
Protobuf runtime	2.16.0	2.17.0	2026-11-13 08:39:21.506
Protobuf generator	2.16.0	2.17.0	2026-11-13 08:39:24.936

Connect 2.3.0, Buf 1.75.0, and Node 24 typings 24.19.2 are the latest releases in their selected lines and are quarantine-eligible. No age-gate bypasses or runtime patches are used.

Validation

• Full yarn ci --concurrency 2 passed under Node.js 24.22.1, including server end-to-end coverage.
• Four focused RPC integration cases passed; Buf schema lint and reproducible code generation passed.
• Immutable install, dependency checks, Syncpack, repository formatting, and stack-specific Beachball checks passed.
• No compatible duplicate RPC dependency trees remain. The generator's exact upstream TypeScript 5.4.5 dependency is kept separate from the repo's TypeScript 6, replacing its previous TypeScript 4.5.2 tree.