Phase 7: authored assets (diagrams, code exhibits, client wall, budget)

Phase 7 is mostly authored assets. This commit is the asset half; the
template half is a Builder child issue because this phase must not write
application code.

DoD items satisfied or advanced:

- [x] Eight diagrams present, both themes, readable at 1x and on mobile
      8 SVGs, one byte-identical <style> block across all 8 (one visual
      language by construction). Light and dark resolve from a single file
      via prefers-color-scheme, verified per file in Chrome: 8/8 return two
      distinct palettes. Geometry verified with getBBox(), not estimated:
      0 findings after fixing 74 (text overflow, partial overlap, empty
      text, out-of-viewBox). Mobile type at the 900px minimum is 14.1/12.2px.

- [x] Six code exhibits with a two-sentence rationale each
      212 verbatim lines across five eras, copied with cp/sed from the
      read-only archive. Every rationale is exactly two sentences about why
      the code is good; every exhibit also carries an honest_note, and where
      the code is not good the note says so (the 3,400-line procedural PHP
      script is presented for its operational judgement, not its structure).

- [~] Every image optimised; total page weight budgeted and recorded
      BUDGET.md records measured raw and gzip weights for all 15 served
      files: 63,802 B raw / 13,220 B gzipped. Zero rasters by design. Page
      weight of a real page is not measurable until Phase 2 templates and
      Phase 3 serving exist, and is recorded as open rather than asserted.

- [x] Archive never linked or exposed
      No mount paths or volume names under content/. Provenance recorded as
      "private archive, path withheld".

- [ ] Client wall reads as deliberate  -> needs markup/CSS (Builder)
- [ ] Lighthouse held at >= 95/95      -> needs a served page (Phase 3)

Also: the client wall is authored as data (45 entries, 44 distinct names) with
the 45-vs-46 discrepancy and the Diajio -> Diageo correction recorded
rather than papered over. No commercial marks are enabled: that is a
permission decision for Sam, so availability is recorded and permission is not
implied.

content/assets/diagrams/07-cost-resource-engineering.svg

@@ -0,0 +1,95 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 960 540" width="960" height="540" role="img" aria-labelledby="ttl dsc">
+<title id="ttl">Cost and resource engineering</title>
+<desc id="dsc">A bar chart of the per-service memory caps drawn to scale against the 1024 MiB ceiling, totalling 970 MiB across four containers, beside the rules that hold the ceiling: equal memory and swap limits, loopback binding, a hard container count and a cost ceiling.</desc>
+<style>
+    text{font-family:ui-sans-serif,-apple-system,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;fill:#1b222b;font-size:15px}
+    .hd{font-size:15px;font-weight:600}
+    .sub{font-size:13px;fill:#5b6673}
+    .cap{font-size:12px;fill:#5b6673;letter-spacing:.06em;text-transform:uppercase;font-weight:600}
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+    .zone{fill:none;stroke:#aab4c0;stroke-width:1.4;stroke-dasharray:7 6}
+    .rule{stroke:#d0d7df;stroke-width:1}
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+    .dot{fill:#6b7684}
+    .tick{stroke:#aab4c0;stroke-width:1.2}
+  @media (prefers-color-scheme: dark){
+    text{fill:#e7edf4}
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+<defs>
+  <marker id="aN" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="mN" d="M0,0 L10,5 L0,10 z"/></marker>
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+</defs>
+  <text x="24" y="40" class="big">Cost and resource engineering — the budget, measured</text>
+  <text x="24" y="68" class="sub">Every service declares a ceiling. The ceiling is a measurement, not an estimate: .13 already runs on 2.3 GiB free with 8.1 GiB of swap in use.</text>
+  <text x="40" y="104" class="cap">per-service cap (MiB)</text>
+  <text x="40" y="136" class="sub">Go app</text>
+  <rect x="200" y="112" width="33.6" height="30" rx="5" class="bar node-a"/>
+  <text x="243.6" y="133" class="sub">120 MiB</text>
+  <text x="40" y="182" class="sub">Qdrant</text>
+  <rect x="200" y="158" width="112.00000000000001" height="30" rx="5" class="bar node-t"/>
+  <text x="322.0" y="179" class="sub">400 MiB</text>
+  <text x="40" y="228" class="sub">Prefect worker</text>
+  <rect x="200" y="204" width="42.00000000000001" height="30" rx="5" class="bar "/>
+  <text x="252.0" y="225" class="sub">150 MiB</text>
+  <text x="40" y="274" class="sub">Guardrail (if local)</text>
+  <rect x="200" y="250" width="84.00000000000001" height="30" rx="5" class="bar "/>
+  <text x="294.0" y="271" class="sub">300 MiB</text>
+  <path d="M200,352 L486.72,352" class="tick"/>
+  <text x="200" y="374" class="sub">0</text>
+  <text x="486.72" y="374" class="sub" text-anchor="end">1024 MiB = the whole new footprint</text>
+  <path d="M200,340 L200,362" class="tick"/>
+  <rect x="200" y="372" width="287" height="56" rx="7" class="node node-t"/>
+  <text x="343.5" y="398.0" class="hd" text-anchor="middle">970 MiB of 1024 MiB</text>
+  <text x="343.5" y="416.0" class="sub" text-anchor="middle">4 containers · measured, not asserted</text>
+  <rect x="520" y="92" width="416" height="336" rx="10" class="zone"/>
+  <text x="532" y="112" class="cap">rules that hold the ceiling</text>
+  <rect x="536" y="118" width="384" height="52" rx="7" class="node "/>
+  <text x="728.0" y="142.0" class="hd" text-anchor="middle">mem_limit == memswap_limit</text>
+  <text x="728.0" y="160.0" class="sub" text-anchor="middle">a service cannot buy headroom from host swap</text>
+  <rect x="536" y="180" width="384" height="52" rx="7" class="node "/>
+  <text x="728.0" y="204.0" class="hd" text-anchor="middle">bind 127.0.0.1</text>
+  <text x="728.0" y="222.0" class="sub" text-anchor="middle">Caddy is the only public listener</text>
+  <rect x="536" y="242" width="384" height="52" rx="7" class="node "/>
+  <text x="728.0" y="266.0" class="hd" text-anchor="middle">4 containers, not 14</text>
+  <text x="728.0" y="284.0" class="sub" text-anchor="middle">one process per job, no sidecars</text>
+  <rect x="536" y="304" width="384" height="52" rx="7" class="node "/>
+  <text x="728.0" y="328.0" class="hd" text-anchor="middle">cost has a ceiling too</text>
+  <text x="728.0" y="346.0" class="sub" text-anchor="middle">median session ≤ US$0.01 · monthly refusal</text>
+  <text x="536" y="384" class="sub">verified with docker inspect, not with intent</text>
+  <rect x="24" y="446" width="912" height="56" rx="7" class="node node-w"/>
+  <text x="480.0" y="472.0" class="hd" text-anchor="middle">Host reality on .13: 15 GiB total · 2.3 GiB free · 8.1 GiB swap in use</text>
+  <text x="480.0" y="490.0" class="sub" text-anchor="middle">exceeding the budget destabilises services people rely on</text>
+  <text x="24" y="524" class="sub">Source: reference/stack.md, hosts measured 2026-10-17. The caps are the contract; the bar chart is the contract drawn to scale.</text>
+</svg>