prose: the key-idea callout — GitHub alerts, one sharp white box; tables hug

The one emphasis device for load-bearing ideas: GitHub-style alert
callouts. The prompt teaches only > [!IMPORTANT] (one device, one
meaning — an unconditional truth laid down, a payoff landed, a hinge
definition) with the restraint law: everything else stays in prose, if
everything is boxed nothing is. The renderer accepts all five GitHub
markers and boxes them identically — a stray [!NOTE] still meant 'this
deserves emphasis', and a marker line must never leak as text.

Rendering (owner rulings): SHARP corners, white stroke, no background,
no label, no icon — just the outline — and the box hugs its text
(width: fit-content capped at the column) instead of stretching
full-width into empty space. Same grammar as the plan blocks: this is
structure, not chrome.

Seam: the Streamdown blockquote override in md-blocks. parseAlertMarker
is pure and exported — Streamdown wraps blocks in its own styled
components, so detection reads the hast node's tagName, and a standalone
marker drops its <br> hard-break artifact along with the empty
paragraph. Plain blockquotes pass through untouched.

Rider (owner, same round): tables hug their contents — width:
max-content on the data-streamdown table (width:auto would still
stretch, the classic table trap); wide ones keep the md-blocks
overflow-x scroller. Graceful in exports: a callout is still a
blockquote there.

6 render pins: the box mounts with white stroke + fit-content + no
rounding, all five markers box, standalone-marker drops the empty
paragraph, multi-paragraph structure kept, plain quotes untouched.

app/globals.css

@@ -353,6 +353,12 @@ body {
    no edge doubles. (md-blocks supplies the wrapper + the copy corner.) */
 [data-streamdown="table"] {
 	border: 1px solid var(--border);
+	/* Tables HUG their contents (owner, callout round 2026-10-07): no more
+	   full-width stretch with dead space. max-content sizes to the cells
+	   (width:auto would still stretch — the classic table trap). No
+	   max-width cap: a max-width would squish-wrap wide tables instead of
+	   letting the md-blocks overflow-x scroller carry them. */
+	width: max-content;
 	/* Tables run at the SESSION prose size (owner note, 2026-09-19: they
 	   visibly lagged the 16px chat text at streamdown's 12.5px text-sm).
 	   Unlayered CSS beats the cells' own utility-layer text-sm, and the