feat(overlay): the behaviour overlay's fixture-buildable half — M1 the block, M2 colour-by modes, M4 provenance and refusal (#397)

[lex00]

Part of #397. Builds the three milestones that can be built against a fixture today — M1 #398, M2 #399, M4 #401 — and stops there. M3 #400, M5 #402 and M6 #403 wait on chant#2355: they need a lexicon that calls an engine (a second call against the planned estate, a call against each of the live and declared halves, a test engine wired into the demo), and no such lexicon exists yet. Stacked on #395 (the audit), which is stacked on #392 (the workbench).

The contract first

The behaviour block's JSON shape is recorded as a comment on #398 and, word for word, on chant#2356, so both repos pin one contract: attrs._behaviour per overlay node (cost per hour, headroom, error rate, resilience, right-size, provenance), meta._behaviour per graph (engine, version, traffic level, an optional engine total, or a refusal), and the same shape as a report document behaviour.<env>.json for tests, demos and CI artifacts.

What landed

M1 (#398) — GET /api/overlay carries the block from the lexicon's node attrs, or from a behaviour.<env>.json report at the member's root when no node carries one, validated field by field and rebuilt to the contract so nothing an engine adds leaks through. meta.behaviour is always present: sourced (with behold's own sums per box and per estate, labelled as sums, and n priced · m unpriced), refusal (every block stripped, the drift overlay untouched), or absent (naming the file and the lexicon path that would supply it). Golden fixtures pin the payload; a test proves an overlay without a block is byte-identical to before.

M2 (#399) — colour by drift, cost or headroom. A card with no block draws the drift overlay's neutral, never the zero end of the scale. One legend per mode; totals per box and per estate in the scope panel, the engine's total when it states one, behold's sum otherwise, labelled either way.

M4 (#401) — every figure carries its provenance badge, engine version · tolerance · basis, with "modeled, not billed" spelled out. A refusal disables the two modes, prints the reason and remedy where the legend was, and leaves drift alone. An absent block disables the modes with the absent line as the tooltip.

Where the numbers come from

Nowhere in behold. The demo ships behaviour.live.json per estate as a recorded fixture whose provenance reads behold-fixture 0 · fixture · modeled on every badge; behold's only arithmetic is the sums, which are labelled as sums. No engine is called, no key is held, nothing is written on anyone's account.

Screenshots (the bundled choudoufu demo, four estates, 45 cards)

colour by drift (the legend from #393, unchanged)	colour by cost

colour by headroom	the scope panel's totals in cost mode

the badge on every figure in the inspect pane	the refusal in place of the modes

Cost is a single-hue ramp (expensive is not a fault); headroom runs red to green because #399 says high headroom good, low headroom bad. Four of the 45 cards carry no block and stay neutral grey in both modes; the legend counts them.

Verification

M1, live on the demo (behold demo choudoufu-estate, choudoufu v0.16.0, floci on 4650): meta.behaviour = { engine: "behold-fixture", version: "0", at: { traffic: "100 rps, p50" }, sum: { perHour: 0.5669, currency: "USD", priced: 41, unpriced: 4 }, boxes: { monolith: 0.2834 · 20/1, team-a: 0.0945 · 7/1, team-b: 0.0945 · 7/2, team-c: 0.0945 · 7/0 } }. With the four report files removed: { absent: "no behaviour block: no node carries attrs._behaviour …, and no report document at monolith/behaviour.live.json, …" }, and the SVG and every _status byte-identical to the priced read.

M2 and M4, in the browser: the nine screenshots above and in docs/src/assets/behaviour/, zero console errors in all four states (priced, absent, refused, drift). The colour ramps are derived from the active theme; the 552-palette sweep found two themes where a naive ramp collapsed (Hot Dog Stand, Grass) and the derivation now walks from the background's lightness, pinned by tests in web/behaviour-scale.test.js.

just check and npm run smoke:ui green at every merge.

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