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wai: ingest the browser capability-negotiation mapping (WebCodecs) #54

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dcharlot wants to merge 2 commits from wai-webcodecs-negotiation into main
pull from: wai-webcodecs-negotiation
merge into: Transaction-Science:main
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dcharlot commented 2026-08-03 06:09:26 -04:00
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Rebased 2026-09-21 onto current main (a800ebe). It had sat since 2026-08-03
and no longer merged: wai/CHANGELOG.md conflicted where both sides appended an
entry. Both entries are kept, the original commit is preserved unchanged
(authorship and date intact), and the reconciliation below is a separate second
commit so review can tell them apart.

SOTA ingest: WAI's §4 dispatch is the browser's own capability primitive —
WebCodecs isConfigSupported(), whose documented fallback is a WASM decoder.
extensions/webcodecs-negotiation.md maps §4 onto a browser sink in two tiers:
native when the platform reports the codec supported, WAI's pure-integer wasm
decoders otherwise, with the classical floor always reachable through wasm.
Informative — it does not change the wire format or the algorithm.

Why the second commit exists

While this sat, extensions/capability-constraints.md landed, which makes
dispatch a precondition check: a sink satisfies a capability when it advertises
cap and the object's declared parameters satisfy a registered constraint
set. Rebased as-is, the two extensions would read as overlapping claims about §4
with nothing saying how they relate.

They are not in tension — the newer one makes this one sharper.
isConfigSupported() is not a codec-string test: it takes a whole
VideoDecoderConfig (codec, codedWidth, codedHeight, …), so the native tier
is already a constraint evaluator, and a browser meets that extension's three
requirements structurally rather than with extra machinery:

capability-constraints.md requires WebCodecs gives
evaluate constraint sets before dispatch isConfigSupported() is pre-flight; it configures nothing
a per-object answer, not per-sink the answer is for that configuration
unsupported, not a decode error supported: false, returned before any payload is committed to

It also returns the normalised config the platform would accept, which is the
accepted parameter set — so a sink SHOULD use that rather than re-derive one.

The limit is stated, not glossed. WebCodecs' parameter vocabulary is the
conventional-media one (codec, resolution, frame rate, bit depth, profile) — the
same shape as the ratified registers capability-constraints.md §3 draws on, and
with the same gap: no WebCodecs configuration describes the neural, quantum,
world or haptic families. Those have no native tier to constrain at all, resolve
through the WASM tier, and stay unconstrained until WAI authors their register
entries. That is the state §3 already describes, not a shortfall introduced here.

Verification

Docs only — wai/CHANGELOG.md, wai/SPEC.md, and the extension. §4/§5
section references were re-checked against current SPEC.md and are unchanged
(§4 Capability dispatch, §5 Registered capabilities). All relative links resolve.
scripts/check-no-vanity-metrics.sh passes.

Correction: the WAI workflows did trigger, and the windows legs will fail

I first wrote here that this touches no source path, so wai-conformance.yml and
wai-byte-equality.yml would not trigger. That was wrong — both ran, and three
windows contexts are present.

The likely cause, from the evidence rather than from Forgejo's source: the paths:
filter appears to be evaluated against the push delta (old head → new head)
rather than the PR's diff against its base. This branch was force-pushed from a
2026-08-03 commit onto 2026-09-20 main, and that delta is 222 files, 15 of them
under wai/wai-rs/ — which matches wai/wai-rs/**. The PR's own diff against
main is the three Markdown files listed above and matches nothing.

So rebasing a stale branch can trigger workflows its content does not touch.
Worth knowing before rebasing anything else that has sat.

The practical consequence is that this PR is now blocked the same way #82 is: the
only runs-on: windows host, cbio-device-0000 (100.98.19.25), has been
offline since ~2026-08-28 — tailscale status reports "offline, last seen 24d
ago", and it does not answer ping, so it cannot be restarted remotely. Its jobs are
never claimed and are eventually cancelled, which the status API reports as
failure with description "Has been cancelled". That is infrastructure, not this
change. Every other leg is green.

🤖 Generated with Claude Code

> **Rebased 2026-09-21** onto current main (`a800ebe`). It had sat since 2026-08-03 > and no longer merged: `wai/CHANGELOG.md` conflicted where both sides appended an > entry. Both entries are kept, the original commit is preserved unchanged > (authorship and date intact), and the reconciliation below is a separate second > commit so review can tell them apart. SOTA ingest: WAI's §4 dispatch is the browser's own capability primitive — WebCodecs `isConfigSupported()`, whose documented fallback is a WASM decoder. `extensions/webcodecs-negotiation.md` maps §4 onto a browser sink in two tiers: native when the platform reports the codec supported, WAI's pure-integer wasm decoders otherwise, with the classical floor always reachable through wasm. Informative — it does not change the wire format or the algorithm. ### Why the second commit exists While this sat, **`extensions/capability-constraints.md` landed**, which makes dispatch a *precondition check*: a sink satisfies a capability when it advertises `cap` **and** the object's declared parameters satisfy a registered constraint set. Rebased as-is, the two extensions would read as overlapping claims about §4 with nothing saying how they relate. They are not in tension — the newer one makes this one sharper. `isConfigSupported()` is not a codec-string test: it takes a whole `VideoDecoderConfig` (codec, `codedWidth`, `codedHeight`, …), so the native tier **is already a constraint evaluator**, and a browser meets that extension's three requirements structurally rather than with extra machinery: | `capability-constraints.md` requires | WebCodecs gives | |---|---| | evaluate constraint sets **before** dispatch | `isConfigSupported()` is pre-flight; it configures nothing | | a per-object answer, not per-sink | the answer is *for that configuration* | | unsupported, **not** a decode error | `supported: false`, returned before any payload is committed to | It also returns the normalised `config` the platform would accept, which is the accepted parameter set — so a sink **SHOULD** use that rather than re-derive one. **The limit is stated, not glossed.** WebCodecs' parameter vocabulary is the conventional-media one (codec, resolution, frame rate, bit depth, profile) — the same shape as the ratified registers `capability-constraints.md` §3 draws on, and with the same gap: no WebCodecs configuration describes the neural, quantum, world or haptic families. Those have no native tier to constrain at all, resolve through the WASM tier, and stay unconstrained until WAI authors their register entries. That is the state §3 already describes, not a shortfall introduced here. ### Verification Docs only — `wai/CHANGELOG.md`, `wai/SPEC.md`, and the extension. `§4`/`§5` section references were re-checked against current `SPEC.md` and are unchanged (§4 Capability dispatch, §5 Registered capabilities). All relative links resolve. `scripts/check-no-vanity-metrics.sh` passes. ### Correction: the WAI workflows did trigger, and the windows legs will fail I first wrote here that this touches no source path, so `wai-conformance.yml` and `wai-byte-equality.yml` would not trigger. **That was wrong** — both ran, and three **windows** contexts are present. The likely cause, from the evidence rather than from Forgejo's source: the `paths:` filter appears to be evaluated against the **push delta** (old head → new head) rather than the PR's diff against its base. This branch was force-pushed from a 2026-08-03 commit onto 2026-09-20 main, and that delta is **222 files, 15 of them under `wai/wai-rs/`** — which matches `wai/wai-rs/**`. The PR's own diff against main is the three Markdown files listed above and matches nothing. So **rebasing a stale branch can trigger workflows its content does not touch.** Worth knowing before rebasing anything else that has sat. The practical consequence is that this PR is now blocked the same way #82 is: the only `runs-on: windows` host, `cbio-device-0000` (`100.98.19.25`), has been **offline since ~2026-08-28** — `tailscale status` reports "offline, last seen 24d ago", and it does not answer ping, so it cannot be restarted remotely. Its jobs are never claimed and are eventually **cancelled**, which the status API reports as `failure` with description `"Has been cancelled"`. That is infrastructure, not this change. Every other leg is green. 🤖 Generated with [Claude Code](https://claude.com/claude-code)
wai: ingest the browser capability-negotiation mapping (WebCodecs)
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4b2bc24087 
SOTA ingest: WAI's §4 dispatch — declare a capability, decode it if advertised,
else fall back — is the exact shape of the browser's own media-capability
primitive, WebCodecs isConfigSupported(), whose established fallback when a config
isn't supported is a WebAssembly decoder. That is WAI's two-tier design already.

New extensions/webcodecs-negotiation.md formalizes it: a browser sink answers §4's
"advertises cap" with isConfigSupported() for the native tier (mapping the floor +
menu codecs to VideoDecoder/AudioDecoder/ImageDecoder), and WAI's pure-integer wasm
decoders as the always-satisfiable fallback — the tier the neural/computed
capabilities (wai.image.jpegai, wai.neural.int_*, …) live in, decoding byte-exact
in-browser (decode-equivalence), and where the classical floor stays always
reachable. It documents what the live /jpegai and /int_hyper sinks already do.
Referenced from SPEC §4; changelog entry. Informative, self-referential — WAI adds a
named capability and a guaranteed wasm floor to the browser's own pattern.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
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