`--config` cannot emit tdbin outputs — codecs go stale under `--watch`

[MelbourneDeveloper]

Problem

--config FILE is the intended "one schema, many outputs" entry point, but its outputs are restricted to converters.LANGUAGES:

// dist/generation-config.js
const languageValue = (value) => converters.LANGUAGES.some((language) => language === value);
const parseOutput = ([language, path]) =>
    !languageValue(language)
        ? err({ message: `unsupported output language '${language}'` })
        : …

tdbin is not a converter language, so there is no way to say "also emit the codec module here" in a config file. tdbin generation has to be driven as separate encode/decode shell-outs, outside the config, outside --watch.

That splits one logical generation step into two mechanisms with two failure modes, and --watch regenerates only half of it — leaving codecs silently stale against the types they encode. Given that the whole point of the LAYOUT_HASH constant is to catch layout drift, having the tooling cause drift on every watched edit is a bad default.

Ask

Make tdbin a first-class config output. Something like:

{
  "source": "docs/models/live-ipc.td",
  "outputs": {
    "rust": "crates/deslop-core/src/wire_generated.rs",
    "typescript": "clients/vscode/src/types/wire-generated.ts"
  },
  "tdbin": {
    "rust": { "path": "crates/deslop-core/src/wire_codec.rs", "mode": "codec-only" },
    "typescript": { "path": "clients/vscode/src/types/wire-codec.ts" }
  }
}

Requirements:

1. --watch regenerates types and codecs from the same parse, so they can never disagree.
2. mode: "codec-only" maps to today's decode behaviour (impls against externally-emitted types); a "full" mode maps to encode.
3. Config-driven runs apply the same emitted-type configuration to both (see the companion issue on codec/config divergence).
4. Deterministic output ordering and the provenance header from Generated output: provenance header (source SHA + version) + built-in --check + deterministic ordering #41 apply to codec files too — a codec module that reorders between runs makes every regeneration a diff.
5. Non-zero exit if the emitted LAYOUT_HASH set changed relative to the file on disk, so CI can gate wire-format changes. This is the tdbin analogue of the --check mode requested in Generated output: provenance header (source SHA + version) + built-in --check + deterministic ordering #41, and it is what actually makes the format's schema-evolution guarantees enforceable rather than aspirational.

Context

Deslop generates Rust + TypeScript from one .td file today via a wrapper script that invokes the CLI once per target and post-processes each. Adding tdbin should add a line to a config file, not a third bespoke code path.

Related: #41 (provenance header, --check, deterministic ordering).