Adds the binary header block that WCF prepends to SizedEnvelope
payloads. Reverse-engineered from .NET probe wire bytes captured via
asb-relay.
Wire form (per the .NET capture analysis in the previous commit):
```
[outer length, multibyte-int31]
[string-1 length, multibyte-int31] [UTF-8 bytes] ← dict id 1 (action)
[string-2 length, multibyte-int31] [UTF-8 bytes] ← dict id 3 (to)
[NBFX <s:Envelope>...]
```
Inside the NBFX envelope, `<a:Action>` and `<a:To>` reference the
pre-pop strings via `DictionaryText 0xAA {odd-id}` instead of inlining
their values. The header strings get assigned odd dict ids
(1, 3, 5, ...); even ids stay reserved for the [MC-NBFS] static dict.
Encode side:
* `encode_envelope` now emits header [action, to] before NBFX. `to_uri`
defaults to empty string when None — caller-supplied `with_to(uri)`
is the supported path.
* AsbClient's `send_envelope` and `send_envelope_one_way` auto-fill
`to_uri` from `self.via_uri` when not set.
* New private `encode_binary_header(strings)` helper.
Decode side:
* New `parse_binary_header_prefix(input)` heuristically detects + parses
the header (look for plausible NBFX element record byte 0x40-0x77 at
the offset implied by the outer length).
* New `resolve_with_header(text, dynamic, header)` resolves
`DictionaryText` with odd id by indexing into header.strings; even
ids fall through to static-dict lookup as before.
Tests pass (72) — round-trip envelope → bytes → envelope recovers
action through the new dict-id resolution path.
Live status: this commit gets us further but the connect SOAP
envelope still TCP-RSTs at SMSvcHost. The remaining delta vs the .NET
capture is structural NBFX optimisation: .NET uses single-letter
prefix-element/attribute records (0x44-0x77 PrefixDictionaryElement
_<a-z>, 0x0C-0x25 PrefixDictionaryAttribute_<a-z>, 0x0B
DictionaryXmlnsAttribute) while our F21 encoder always uses the long
forms (0x43 prefix-string + name-dict-id, etc.). Logically
equivalent but WCF's parser likely strict on which form it accepts.
Next iteration will add short-form encoding to F21 for single-letter
prefixes (s:, a:, h:, i:) which covers every namespace prefix in our
envelope.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
2867310817