[Superseded by #204] Widen SessionStatus to a u32 bitset (Rust + Kotlin) — SemVer-major

[joshmouch]

🔁 Superseded by #204 (closed 2026-06-10 — not abandoned). #204 carries the same SessionStatus u32 bitset widening (Rust + Kotlin) plus the shared round-trip corpus, and is current with main. This branch was opened on a pre-#211 base, so against current main it would revert #211's reducer _meta propagation; the bitset work has been consolidated into #204 instead.

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Widen SessionStatus to a u32 bitset (Rust + Kotlin) — SemVer-major

SessionStatus is an unsigned 32-bit wire bitset: named status flags combine bitwise, and a newer host can set forward-compat bits a client version doesn't model yet. To round-trip those bits losslessly, the in-memory type must be able to hold any u32. The previous Rust #[repr(u32)] enum (a closed set) and Kotlin Int (signed — overflows at bit 31) couldn't, so unknown/combined bits were silently dropped on decode→re-encode.

This widens both as one logical change:

• Rust: SessionStatus becomes struct SessionStatus(pub u32) with named flag constants — combine with |, test membership with .contains(..), read the raw value (including unknown forward-compat bits) with .bits().
• Kotlin: SessionStatus.rawValue becomes Long (was Int); flag constants are Long literals; serialized as a JSON number.

Both are SemVer-major.

Review note: the types/test-cases/round-trips/ fixtures in this diff are shared with #204 (byte-identical) and deduplicate on merge — they're best reviewed there. This PR's unique change is the widening itself: clients/rust/, clients/kotlin/, scripts/generate-{rust,kotlin}.ts. The two PRs are independent and merge cleanly in either order; this one closes the Rust/Kotlin round-trip gaps against fixtures 004/005/016.

Verification

client	result
Rust	cargo test 72 passed · cargo fmt --check clean · cargo clippy clean
Kotlin	gradlew test --rerun-tasks — 254/254

[joshmouch]

Closing in favor of #204.

This branch was opened before #211 (reducers: propagate tool call action metadata) landed on main, so when diffed against current main it reverts #211's _meta propagation across TypeScript (types/channels-session/reducer.ts — removes the tcBaseWithMeta helper), Go (clients/go/ahp/reducers.go), and Swift (Reducers.swift), and removes the associated reducer fixtures (deletes 220-toolcall-actions-update-meta.json; strips _meta expectations from 026/070).

#204 carries the same SessionStatus u32 bitset widening (Rust + Kotlin) and the shared round-trip corpus, is current with main (includes #211), and leaves the reducer _meta work intact. Consolidating the bitset + corpus work there.