feat(tx3c): generate the first-party Swift client with --template swift-client

[scarmuega]

Implements plans/lang-codegen-swift-client.md (decisions 0015 and 0016): the first-party Swift client ships inside tx3c as the built-in template swift-client.

What it renders

tx3c codegen --template swift-client emits a standalone SwiftPM package: Package.swift, README.md, and Sources/<ProtocolName>Client/{Client,Types}.swift, where the package, product, module and facade are all <ProtocolName>Client.

• Types.swift: the merged Swift backend's declarations (Sendable structs, enums with associated values, keyword escaping, deterministic collision errors). Every record, tuple and variant now spells its own argValue: ArgValue property, mirroring the SDK's encoder (records as constructor 0 in declared order, variants by case index, tuples positional, maps as key-sorted pairs).
• Client.swift: PROTOCOL_NAME / PROTOCOL_VERSION / TARGET_TII_VERSION, one public <TX>_TIR envelope per transaction, one private <PROFILE>_PROFILE SDK Profile value per profile, a nested Profile enum when profiles exist (init(options:profile:), otherwise init(options:)), typed with<Party> setters routed through withPartyUnchecked, and one typed transaction method per tx that constructs ArgValue values statically and calls argTagged. No TII, schema, ParamType or dynamic loader is embedded.
• Package.swift: depends on Tx3SDK from tx3-lang/swift-sdk from: "0.15.0", plus attaswift/BigInt from: "5.7.0" (the SDK's pinned version) only when integers appear. Every generated file states the v1beta0 target and the source tii.version.

Codegen changes

• Templated output paths lay out Sources/{{identifier tii.protocol.name 'swift' 'type'}}Client/. The path uses single-quoted Handlebars literals because the release workflow checks the repository out on Windows, where " cannot appear in a file name.
• The planner records an Encoding next to every member's type and resolves component aliases to their targets once all components are planned. The Swift backend spells conversions from it; templates never branch on schema shapes.
• New helpers: argValue <tii> <transaction> <param> <language> <params-expr> (spelled from the same plan as the params declaration, so it always matches the declared field types), profile <profile> <language> (the SDK Profile value), and usesModule <tii> <language> <module>.
• Golden output added for the transfer, complex and edge fixtures under expected/swift-client/. The existing custom/swift, custom/compat-swift and custom/templated-paths goldens gain the argValue properties (additive only).

CI compile check

codegen compile (swift-client) runs on macos-15 with Xcode 16.4, the swift-sdk repository's own baseline. No swift-sdk 0.15.0 tag exists yet, so the script clones tx3-lang/swift-sdk at 02fa0f2cc70d38f2623141035b3eb18509854b9a, tags that commit 0.15.0 locally and points a SwiftPM mirror at the clone; the generated Package.swift is then built exactly as rendered. swift package edit --path was tried first but SwiftPM resolves before editing and fails on the missing tag. Once the tag exists, the block in .github/scripts/codegen-compile-check.sh is deleted and the check resolves the published release directly (tracked in the Swift initiative plan).

Verification

• cargo fmt --all -- --check, cargo clippy --workspace --all-targets --all-features --locked -- -D warnings, cargo test -p tx3c --locked: pass.
• .github/scripts/codegen-compile-check.sh swift-client: transfer and complex render and swift build against the pinned SDK commit (Swift 6.2.3 locally).
• Rendering each fixture twice gives byte-identical output.
• A consumer package in a temporary directory with no .tii file constructs UnknownClient for every profile, binds all three parties, and gets a TxBuilder from transfer(_:); it constructs ComplexTypesClient(options:profile: .local) and asserts ComplexParams(...).argValue == ArgEncoder.encode(sameNativeValue, as: ParamType.fromJSONSchema(...)), including a unit variant case. The edge fixture (no parties, no profiles) pins the no-profile constructor in the golden corpus.
• Fixture hashes match the plan: transfer 8d5d715f…da31, complex 0a7195b2…ae83.

🤖 Generated with Claude Code

[scarmuega]

QA (code-qa) review at head 2ca43858d1133279b2f6cdee97ac25b53494feeb.

One correcting commit pushed, 2ca4385 — fix(tx3c): cut alias cycles that pass through lists and maps. The new resolve_components only detected an alias that aliased itself directly; a hand-written TII with "Loop": { "type": "array", "items": { "$ref": "#/components/schemas/Loop" } } overflowed the stack for every template (ts-client included), where the base revision rendered typealias Loop = [Loop] and moved on. The visited path now follows the member through list and map items, an alias declaration starts with its own name on the path, and a unit test covers the direct, aliased-alias and map-nested cases. Goldens are unchanged.

Everything else verified as delivered: cargo fmt, clippy -D warnings, cargo test -p tx3c --locked (41 unit + golden); codegen-compile-check.sh swift-client builds transfer and complex against the pinned SDK commit with Swift 6.2.3; the generated argValue rules match ArgEncoder at 02fa0f2 (record → constructor 0 in declared order, variant → case index, tuple positional, map key-sorted, unit → empty constructor 0); TARGET_TII_VERSION follows the other templates' convention. PR stays draft; readiness is published by the runtime after QA is recorded.

[scarmuega]

Merge observed.

Plan: plans/lang-codegen-swift-client.md
QA-approved head: 2ca43858d1133279b2f6cdee97ac25b53494feeb

Trellis will verify the human merge evidence, adopt the domain pin, and retire the plan. No further merge action is needed.