1.8: generator PoC tools/aimux-codegen: ToolCall -> TS + Go, --check (on #42)

[cunninghamcard-bit]

Phase 1 unit 1.8: a generator proof of concept (arcships#200:1509; RFC-0042 T5). Stacked on #42 (1.7, exp/u1.7-descriptor-schema @ b8d8261); the PR base is that branch.

Added: tools/aimux-codegen (new workspace member)

• Input: spec/ToolCall.json, a data-only type spec giving the name, docs, and for each field its wire name, type and whether it's optional. Unknown keys are rejected.
• Library: render_ts, render_go, generate, write, check.
• Binary: aimux-codegen writes generated/. aimux-codegen --check regenerates in memory and exits non-zero if any committed file is missing or differs.
• Committed outputs:
  • generated/ts/ToolCall.ts
  • generated/go/tool_call.go (package aimuxgen, encoding/json tags, gofmt-clean)
• There is no build.rs and no second copy of the spec (docs: full-chain AI SDK alignment design and impact map arcships/aimux#200 §6.5). Nothing is wired into the bindings yet; ts-rs is unchanged.

Acceptance (tools/aimux-codegen/tests/codegen_test.rs, 8 tests)

• Wire matches the current binding: typescript_matches_the_current_binding_type. The generated TS equals bindings/node/src/types/ToolCall.ts line for line below the one-line header: same fields, optionality, types, imports and docs.
• Go wire: go_struct_round_trips_core_tool_call_json.
  • Four samples are serialized by aimux_core::tool::ToolCall (static, dynamic + providerExecuted, providerMetadata, invalid + error).
  • The generated Go struct decodes and re-encodes each one, and the result must be the same JSON value (go test in a temp module, stdlib only).
  • The test also asserts the Go file is gofmt-clean.
  • It ran here with go 1.24.4. Without go on PATH it prints SKIPPED.
• --check catches tampering:
  • check_rejects_tampered_typescript: changing dynamic?: to dynamic: fails.
  • check_rejects_tampered_go: changing the toolName tag fails.
  • Both go through both the library and the binary (non-zero exit, "out of date").
  • check_rejects_a_missing_file covers a deleted output.
  • check_passes_on_an_untouched_copy exits 0, and committed_outputs_are_up_to_date checks the committed files.
• spec_rejects_unknown_fields.

Fixture and cassette diff: zero.

Results (local linux x64)

	1.7 (#42)	1.8
cargo test --workspace	2875 / 0 / 7	2883 / 0 / 7 (+8)
fmt / clippy -D warnings	ok	ok
boundary script	0	0
gen_ts_types --check	ok	ok
Node ava (node 22)	87 / 1 baseline fail	87 passed, same 1 failure

Python was not run (no venv). This is a PoC for one type. Unions or discriminators, and the other six languages, are not covered.