feat(generator): an optional special number keeps its named literals through the tri-state wrapper

[Blind-Striker]

The generator now emits a working tri-state member for an optional-and-nullable request property whose number admits NaN and the infinities. Until now, OptionalConverterNamePolicy threw "No optional converter name exists for plan 'SpecialNumberTypeReferencePlan'". Generated output at the 2.0.29 pin is byte-identical: no pinned member has this shape. The 2.0.32 pin needs it for VoiceWebRTCTransportInput.dcid (Schema.optional(Schema.Number) in packages/protocol/src/groups/voice.ts:8).

Part of #462. This is REFRESH-232 PR A, the generator half of the 2.0.29 → 2.0.32 pin refresh. PR B, the refresh itself, follows on a base that contains this one.

What changes

• OptionalConverterNamePolicy: a top-level special-number instantiation is named OptionalOfSpecialNumberJsonConverter. A special number inside a list or dictionary still throws the existing message, because a container's converter would go through the plain double metadata and lose the named literals.
• OptionalConverterEmitter:
  • The de-duplication key becomes the pair (formatted type, converter name). Both representations format as double?, so a format-only key would merge them into one converter. With the pair key, two different types that share a converter name still reach SourceEmitter's duplicate-path refusal.
  • The special converter reads a JSON string that is ordinal-equal to NaN, Infinity or -Infinity as that value, and refuses any other string with a JsonException. It writes those three values back as the same strings. Null and number handling are as before.
• ModelEmitter: a wrapped member no longer carries [JsonNumberHandling]. On an Optional<double?> member, System.Text.Json throws at metadata time: "'JsonNumberHandlingAttribute' is only valid on a number or a collection of numbers". So the converter carries the named literals instead. Required and non-wrapped optional special numbers keep the attribute unchanged.
• Canon: one clause in docs/architecture/protocol-and-generation.md, in the tri-state converter bullet.
• CHANGELOG: no entry, since nothing consumer-visible changes at the pin. PR B's 2.0.32 entry covers the member that uses this.

The converter matches what System.Text.Json's AllowNamedFloatingPointLiterals does on a required member. Measured on net10.0 with a source-generated context: it writes NaN as "NaN", and it refuses "nan", "1.5" and "+Infinity".

Tests

• Red first:

  • inventory: a wrapped plain double? and a wrapped special number give exactly two converters, in order;
  • container refusal: a wrapped list or dictionary of special numbers is still refused, with the full message;
  • duplicate-path refusal: two types that share a converter name still reach the refusal (in SourceEmitterTests);
  • attribute placement: required and plain optional special numbers keep [JsonNumberHandling], and the wrapped one doesn't (in ModelEmitterTests);
  • compiled matrix round trip: a patchSpecialNumber member in the materialization matrix's request schema covers absent, explicit null, 4.5, and each named literal (exact JSON text). "nan", "+Infinity" and "1.5" each throw JsonException.

• Mutation: seven compiling mutants, all killed, each production file restored and compared byte-for-byte:

  Mutant	Killed by
  format-only de-duplication key	inventory row
  the read falls through to GetDouble	matrix
  the write falls through to WriteNumberValue	matrix (ArgumentException on NaN)
  [JsonNumberHandling] kept on the wrapper	matrix (InvalidOperationException) and the attribute row
  case-insensitive literal match	matrix ("nan")
  special numbers admitted inside containers	container rows
  converter-name-only key	duplicate-path row

• Existing-test edits: only additions. In the materialization matrix:

  • the request schema gains patchSpecialNumber;
  • the request-member assertions gain its wrapper, type and nullability;
  • the cleared payload and its null loop gain the member.

  Every existing assertion is unchanged.

Budget (against the merge-base)

• Hand-written tools: 48 added lines and 3 removed, against a cap of 70.
• Tests: 107 added lines, against a cap of 140 (one line removed).

Local check and review

• Local check at this head on dev-01, on a quiet host, after a root Release build: slopwatch 0 issues; the Release build with 0 warnings; both format passes; verify-clones passing; --help; generate --verify current; the whole Tools.Tests project at 2086/0, Packaging included. CI is the full gate.
  • Bun 1.4.3, off the 1.4.2 pin.
• Harness verify: the guards, the five touched classes, the whole Tools.Tests project (2072/0), verify-clones, generate --verify and the whitespace pass.
• Review: the coordinator's Claude review and a fresh cross-family review. Neither found a behaviour defect. Both flagged test placement, and this PR fixes it: the source-emitter and model-emitter rows moved to their subjects' classes.
• Coordinator nits, fixed here:
  • the converter's JsonException now carries a message;
  • the canon names the three literals;
  • the literal table has a summary.

Provenance: Generator lane / opencode dispatch harness (openai/gpt-6.1-sol-1m), coordinated, reviewed and finished in Claude Code.