feat(web): unify tool-row expand interaction with IN/OUT card and trajectory Inspect

Every expandable tool row shares one interaction (whole-row toggle,
icon-to-chevron hover preview) and one expanded body: an IN/OUT
gutter-labeled card with per-section 150px scroll caps and sticky labels.
toolRowModel derives result output and the error first line, terminalFailed
surfaces a failing exit as the collapsed row's red dot, a hover Inspect
pill jumps to the call's trajectory record through a one-shot store
handoff, and the chat view keeps its scroll offset across view switches.

packages/client/ui-primitives/src/TerminalBlock.module.css

@@ -7,6 +7,10 @@
 .block {
   --dsl-terminal-radius: 12px;
   --dsl-terminal-line-height: 22px;
+  /* Rebindable by consumers (CodeBlock's --dsl-code-block-content-font
+     pattern): a surface wanting the smaller code size rebinds this together
+     with --dsl-terminal-line-height on its own container. */
+  --dsl-terminal-font: var(--dsw-font-markdown-code-block);
   /* The card's own left inset, holding the run-state dot in a column of its own
      so it never competes with the commands for horizontal space. */
   --dsl-terminal-gutter: 30px;
@@ -22,26 +26,49 @@
   color: var(--dsw-alias-label-primary);
   background: var(--dsw-alias-markdown-code-block);
   border-radius: var(--dsl-terminal-radius);
+  /* Clip the banner to the card's own radius: when a consumer adds a border,
+     the banner's equal corner radius no longer nests inside it and leaves a
+     notch at the corner. Nothing inside renders out of the box. */
+  overflow: hidden;
 }
 
-/* Top-aligned: the status pill and copy control stay on the first prompt row
-   however many command lines the card carries. */
+/* The status pill and copy control top-align to the FIRST prompt row (their
+   heights are capped to the prompt line, so on a multi-line command they sit
+   with the first command instead of floating mid-banner). */
 .header {
   display: flex;
   align-items: flex-start;
   gap: 12px;
-  /* Pulled back across the card's gutter padding so the banner background and
-     its top-left radius span the FULL surface, then re-inset by the same amount
-     so the prompt text and the dot keep their positions. A plain block child
-     only reaches the content box, which left the gutter column painted in the
-     body color and drew the card's top-left corner in it — invisible in the
-     light theme, where banner and body share a token, and visible in the dark
-     one, where they do not. */
+  /* Pulled back across the card's gutter padding so the banner spans the FULL
+     surface, then re-inset by the same amount so the prompt text and the dot
+     keep their positions. The banner shares the card's own surface (no banner
+     token): the l2 divider below is the section boundary. */
   margin-left: calc(-1 * var(--dsl-terminal-gutter));
   padding: 9px 14px 9px var(--dsl-terminal-gutter);
-  background: var(--dsw-alias-markdown-code-block-banner);
   border-top-left-radius: var(--dsl-terminal-radius);
   border-top-right-radius: var(--dsl-terminal-radius);
+  /* A long multi-line command scrolls inside the banner (same cap as the
+     IN/OUT card's sections) instead of pushing the output off screen. */
+  max-height: 150px;
+  overflow-y: auto;
+}
+
+/* Banner scrollbar floats off the card edge like the output's. */
+.header::-webkit-scrollbar-thumb {
+  border: 2px solid transparent;
+  background-clip: padding-box;
+  border-radius: 6px;
+}
+
+.header::-webkit-scrollbar-track {
+  margin: 6px;
+}
+
+/* Full-width l2 hairline between the command banner and the body — the same
+   divider the IN/OUT card draws between its sections. A running card is
+   banner-only, so it draws none. */
+.block:not([data-running]) .header {
+  border-bottom: 1px solid var(--dsw-alias-border-l2);
 }
 
 /* One row per command line. The prompt column is the only element allowed to
@@ -51,7 +78,7 @@
   flex-direction: column;
   min-width: 0;
   flex: 1;
-  font: var(--dsw-font-markdown-code-block);
+  font: var(--dsl-terminal-font);
 }
 
 .promptLine {
@@ -100,27 +127,59 @@
   white-space: pre;
 }
 
+/* Capped to the prompt's line height (Pill's own 24px height would exceed a
+   smaller-font prompt row and stretch the banner). Sticky against the
+   banner's own scroll so the pill and the copy control stay in reach while a
+   long command scrolls underneath. */
 .status {
   flex: none;
+  position: sticky;
+  top: 0;
+  height: var(--dsl-terminal-line-height);
   color: var(--dsw-alias-state-error-primary);
 }
 
 .copyButton {
   flex: none;
-  background-color: transparent;
+  position: sticky;
+  top: 0;
+  /* Card surface, not transparent: the control is sticky over the banner's
+     own scroll, so scrolled command text must not bleed through it. */
+  background-color: var(--dsw-alias-markdown-code-block);
   border: none;
   padding: 0;
   margin: 0;
   color: var(--dsw-alias-label-secondary);
   cursor: pointer;
   font: var(--dsw-font-xs-13);
+  line-height: var(--dsl-terminal-line-height);
 }
 
+/* Vertical scrolling lives on the OUTPUT, not the card root: a root scroller
+   would run its scrollbar over the banner (and the copy control), while here
+   the banner stays pinned and the bar sits inside the output's right padding.
+   Unset, the max-height is none and the auto overflow never engages. */
 .output {
+  max-height: var(--dsl-terminal-output-max-height, none);
   padding: 12px 14px 12px 0;
-  font: var(--dsw-font-markdown-code-block);
+  font: var(--dsl-terminal-font);
   overflow-x: auto;
-  overflow-y: hidden;
+  overflow-y: auto;
+}
+
+/* Both output scrollbars (vertical cap, horizontal pre overflow) float 2px
+   off the card edge: a transparent border clips the thumb inward so it never
+   hugs the rounded corner. */
+.output::-webkit-scrollbar-thumb {
+  border: 2px solid transparent;
+  background-clip: padding-box;
+  border-radius: 6px;
+}
+
+/* Track end-margins keep the thumb's travel out of the card's rounded
+   corners in both directions. */
+.output::-webkit-scrollbar-track {
+  margin: 6px;
 }
 
 /* No wrapping, no word-break: alignment is the payload of terminal output. */
@@ -147,6 +206,6 @@
 
 .empty {
   padding: 12px 14px 12px 0;
-  font: var(--dsw-font-markdown-code-block);
+  font: var(--dsl-terminal-font);
   color: var(--dsw-alias-label-tertiary);
 }

packages/client/ui-primitives/src/TerminalBlock.tsx

@@ -35,7 +35,7 @@ export interface TerminalBlockProps {
   signal?: string | undefined
   /** The command is still running: the block shows the prompt line alone. */
   running?: boolean | undefined
-  /** Height cap in output lines before the middle collapses (default {@link DEFAULT_TERMINAL_MAX_LINES}). */
+  /** Height cap in output lines before the middle collapses (default {@link DEFAULT_TERMINAL_MAX_LINES}); Infinity disables the cap. */
   maxLines?: number | undefined
   /** Extra class merged onto the wrapper (callers position; this component draws). */
   className?: string | undefined