Make the generate lane snappy: self-contained playbook, fast-path poll instructions

The maintainer's field run took five and a half minutes from the prompt
to variants on screen. Two baseline runs on the same repo reproduced it
(356 s mean): 68 KB of skill text read before the first variant (a 36 KB
live.md among it), six to ten tool calls spent finding the dev URL and
the selector, 9 to 10 KB of variants carrying tune knobs, and a document
read plus a detect pass after the accept.

generate.md is now the whole contract for the lane and never sends the
agent to live.md, craft-floor.md, or the action reference on the happy
path; the floors are inlined. The engine carries the rest: a generate
started by live-generate is journaled and queued with origin "agent",
and its poll instructions hand out the fast path (identity from the
event's computed styles and custom properties, the action's three
dimensions, no knobs unless asked, one edit, reply done) instead of the
interactive planning pointer. `impeccable live --allow-missing-context`
boots without PRODUCT.md or DESIGN.md, naming what is missing, so the
lane never falls into the init interview; the boot also reports devUrl,
the origin whose page carries the injected tag, so the agent opens the
page instead of reading terminals. Accept is a bake and live-complete is
its verification: no detect pass, no document read.

Three trimmed runs (one without any context files) averaged 179 s from
prompt to variants, 21 tool calls and 106k tokens against the baseline's
356 s, 30 tool calls and 144k tokens; the accept bake went from 67 s to
41 s. Method and numbers: tmp/questionaire/plan41-field-tests/SNAPPY-REPORT.md
in the maintainer's checkout.

Tests: dev_url probe unit tests, a fast-path instructions unit test, the
origin marker in the protocol suite, and tests/live-boot-fastpath.test.mjs
(flag, contextMissing, devUrl through a stand-in dev server); contract doc
updated.

Written with AI assistance (Claude).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/test-suites.mjs

@@ -141,6 +141,7 @@ export const SUITES = {
       /^tests\/live-e2e\//,
       /^tests\/lib\/engine-bin\.mjs$/,
       /^tests\/live-agent-target\.test\.mjs$/,
+      /^tests\/live-boot-fastpath\.test\.mjs$/,
     ],
     commands: [
       {
@@ -148,6 +149,7 @@ export const SUITES = {
         files: [
           'tests/live-reference.test.mjs',
           'tests/live-agent-target.test.mjs',
+          'tests/live-boot-fastpath.test.mjs',
           'tests/live-browser-ignores.test.mjs',
           'tests/live-browser-source.test.mjs',
           'tests/live-e2e-agent-output.test.mjs',