docs(ai): ai.md becomes a router; invariants move to AGENTS.md; budgets gated

ai.md 228 → 64 lines. It now carries only: what the product is, the build
commands, the architecture table, a "where the truth lives" table, and a
pointer to HANDOFF. No narrative, no status, no duplicated invariants.

AGENTS.md (195 lines) is now the single always-read file:
- the 20 invariants that break output, wipe user data, or ship a legal/trust
  breach — one line each, pointing at the doc that explains it (they replace
  110 lines of invariant stubs that duplicated docs/ai/*.md verbatim)
- Response style + No-Fluff Mode moved in from ai.md (rules belong in the rules file)
- onboarding is now: HANDOFF → ai.md router → the ONE docs/ai file → dir index;
  TASKS.md is read when the question is "what's next", not to write code
- memory rides with the change but is no longer a unit of its own; HANDOFF is
  ≤40 lines and overwritten, never appended

Anti-rebloat gate: scripts/verify.sh gains step 1/4, a doc-budget check
(AGENTS ≤210, ai ≤100; HANDOFF/TASKS caps land with the queue trim). A commit
that pads a capped file instead of moving detail fails the gate.

schema.md and docs/index.md corrected for the new roles and reading order.
Docs-only unit: scope-check run, no build.

scripts/verify.sh

@@ -8,7 +8,8 @@
 # against fresh compiler output.
 #
 # Requires WINDOWS dotnet (never Linux dotnet — it re-downloads the windowsdesktop packs
-# over the slow 9p bridge; see ai.md -> Run). Reads the Windows path from the WSL mount.
+# over the slow 9p bridge; see docs/ai/environment.md -> Run). Reads the Windows path from the
+# WSL mount.
 
 set -euo pipefail
 
@@ -18,7 +19,24 @@ DOTNET="/mnt/c/Program Files/dotnet/dotnet.exe"
 ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 ROOTWIN="$(wslpath -w "$ROOT")"
 
-echo "══ 1/3  CLEAN BUILD (expect 0 warnings) ══"
+echo "══ 1/4  DOC BUDGETS ══"
+# The map stays cheap to read. A commit that PADS a capped file instead of replacing or
+# moving detail fails here (see AGENTS.md -> Reading budget).
+check_budget() {
+    local rel="$1" cap="$2" lines
+    [ -f "$ROOT/$rel" ] || { echo "✗ $rel is missing"; exit 1; }
+    lines=$(wc -l < "$ROOT/$rel")
+    if [ "$lines" -gt "$cap" ]; then
+        echo "✗ $rel is $lines lines (cap $cap)."
+        echo "  Move the detail to docs/ai/<subsystem>.md, MyMistakes.md or git log — do not pad."
+        exit 1
+    fi
+    printf "  ✓ %-12s %3s/%s lines\n" "$rel" "$lines" "$cap"
+}
+check_budget "AGENTS.md" 210
+check_budget "ai.md" 100
+
+echo "══ 2/4  CLEAN BUILD (expect 0 warnings) ══"
 "$DOTNET" clean "$ROOTWIN\\ytLive.csproj" > /dev/null
 OUT="$("$DOTNET" build "$ROOTWIN\\ytLive.csproj" 2>&1)"
 if echo "$OUT" | grep -qI ": warning"; then
@@ -29,7 +47,7 @@ fi
 echo "$OUT" | grep -E "Build succeeded" || { echo "$OUT" | tail -5; exit 1; }
 echo "✓ Build clean, 0 warnings."
 
-echo "══ 2/3  TEST SUITE ══"
+echo "══ 3/4  TEST SUITE ══"
 TESTDLL="$ROOTWIN\\ytLive.Tests\\bin\\Debug\\net8.0-windows10.0.19041.0\\ytLive.Tests.dll"
 "$DOTNET" build "$ROOTWIN\\ytLive.Tests\\ytLive.Tests.csproj" > /dev/null
 set +e
@@ -52,7 +70,7 @@ if [ "$TEST_EXIT" -ne 0 ]; then
     echo "⚠  Test exit=$TEST_EXIT but only the 2 known pre-existing failures present (OK)."
 fi
 
-echo "══ 3/3  SCOPE CHECK ══"
+echo "══ 4/4  SCOPE CHECK ══"
 "$ROOT/scripts/scope-check.sh" "$@"
 
 echo ""