Empirically verified against a live full Lighthouse run of www.sim.ai
(production, pre-fix) plus a local build of the exact deployed commit with
source maps temporarily enabled for root-causing. Distinguished genuinely
failing audits from passing ones already misread as broken.

- fetchPriority missing on every LCP hero image: `priority` generates a
  preload <link> but Next does not auto-add fetchpriority=high to it -
  confirmed via raw deployed HTML diff. Added explicit fetchPriority='high'
  to all 5 priority Image usages (hero, enterprise, blog/library post +
  index cards).
- valid-source-maps failing: production ships no source maps at all
  (productionBrowserSourceMaps defaults false). Enabled it - safe here since
  this repo's frontend is already fully open source, so no incremental
  exposure versus Next's default.
- image-delivery-insight (55.8KB wasted): feature-integrate-ui.png's `sizes`
  hint was a flat 1050px regardless of viewport, so mobile fetched the
  1920w variant for a ~423px real render. Replaced with a responsive sizes
  expression derived from the sibling backdrop image's own (already
  correct) hint, scaled by the callout's documented 125% overhang.
- cache-insight (best-fixable portion): _next/static/* filenames are
  content-hashed and immutable per deploy, but shared one cache rule with
  unhashed /public assets, capping both at 1-day max-age. Split into two
  rules - hashed assets now get 1-year immutable, unhashed assets keep the
  shorter revalidating TTL. Verified via a real build + server that both
  paths now return the correct distinct header.

Investigated and NOT changed (documented, not assumed):
- legacy-javascript-insight (14KB): traced via sourcemap to
  next/dist/build/polyfills/polyfill-module.js - Next's own built-in
  polyfill bundle, not our code or a dependency, and not exposed via any
  next.config.ts option. No browserslist misconfiguration on our end (none
  exists; Next already defaults to its modern target).
- forced-reflow-insight: even with source maps present locally, the
  dominant cost (335-417ms) stayed [unattributed] by Chrome's own profiler,
  and the small attributed slice was non-deterministic between our own
  chunk and a third-party script (HubSpot analytics) across runs - not a
  confident single root cause worth a targeted fix.
- render-blocking-insight / network-dependency-tree / bf-cache: bf-cache's
  actual failure reason is Cache-Control: no-store on the main document -
  the exact root cause already fixed on staging (PR #5522/#5528, the
  PublicEnvScript/unstable_noStore fix) but not yet promoted to main/prod.
  Resolves once that ships, not additional work here.

…6s -> 2.8s)

Ran a full Lighthouse sweep across every public page as requested. /blog
scored 73 (LCP 6.6s) while every other page scored 95+ - reproduced
consistently across 3 runs, not noise. Traced via lcp-breakdown-insight:
the LCP image (mothership/cover.png, 241KB even after the earlier palette
compression pass) took 6+ seconds to download on simulated mobile
throttling, well beyond what its size should cost.

PNG is a poor fit for this illustration's subtle gradients versus JPEG's
lossy compression. Verified empirically before converting: same 1920x1080
resolution, visually identical (spot-checked), 241KB -> 65KB (73% smaller).
No other cover in the content set uses PNG and benefits the same way
(checked copilot/cover.png, the only other PNG cover - already optimal at
64KB, converting it yielded no improvement, left unchanged).

Verified fix: /blog score 73->93, LCP 6.6s->2.8s, reproduced across 3 runs.

- integrations-callout: account for FeatureCard's max-lg:grid-cols-1 mobile
  stack in the sizes hint, verified against Lighthouse's measured mobile
  render width.
- next.config: remove a custom _next/static cache-control rule that never
  actually fired (confirmed via header-marker test) - Next's own built-in
  default already applies the correct immutable 1yr cache to that path.

- integrations-callout: derive sizes from the section's actual grid math
  (fixed 386px copy column, 40px gap, section gutters) instead of an
  approximated vw fraction. Verified against a static reproduction of the
  layout rendered at each Tailwind breakpoint - the old 110vw mobile tier
  underestimated real render width by ~3% right at the 1023px stack
  boundary, which could cause the browser to pick a too-small srcset
  candidate and upscale.
- next.config: the .map header rule's trailing `$` was read as a literal
  character by Next's path-to-regexp source matcher, not a regex anchor,
  so the rule never matched a real .map URL (confirmed via routes-manifest
  regex + a live header check). Removed the dead anchor and added a
  bounded Cache-Control so a future decision to stop shipping source maps
  isn't undermined by a 1yr immutable cache on already-fetched maps.

…c files

Both the marketing site and docs site's llms.txt validator errors ("does
not appear to contain any links") traced to the same root cause: a static
public/llms.txt shadowed a better-written, already-existing dynamic
app/llms.txt route, and every "link" in the static files (and in the
docs app's auto-generated route) was bare `label: url` text, not Markdown
link syntax - so a strict Markdown-link parser found zero matches even
though URLs were visibly present.

- apps/sim: delete public/llms.txt (dead code, shadowing the properly
  Markdown-linked app/llms.txt route.ts, confirmed via production headers
  showing the static file was what actually served). Fix llms-full.txt's
  Links/Support/Legal sections to use [label](url) syntax, correct a
  stale "Next.js 15" reference, and replace "Mothership" with "Chat" per
  the constitution's language rules.
- apps/docs: same shadowing issue - delete the orphaned public/llms.txt
  (also still said "Mothership"). Fix the auto-generated per-page link
  list in app/llms.txt/route.ts to emit [title](url) instead of
  "title: url" for every documentation page.