fix(web): keep escapes, UNC roots, and truncated cwd honest

Four review findings. Two are defects the previous two rounds introduced,
which the existing tests did not catch:

A backspace erased raw bytes, so one landing after an SGR reset ate part of
the escape: `\x1b[31mabc\x1b[0m\b\bXY` left `\x1b[` and repainted the rest of
the line with whatever the remainder parsed as. Backspaces now resolve over
VISIBLE characters — a CSI sequence is one indivisible unit a backspace steps
over on its way to the last printed character, so the surviving text keeps
the color its run authored.

The cwd normalizer popped a UNC share root: `\\server\share` with a `..`
became `/server`, losing the separators too. A UNC path's server and share
are its root, and Windows cannot climb above a share, so they are split off
and the remainder collapses against that root.

The other two are gaps the earlier fixes left:

The render-site fallback row still passed the args-derived summary, so any
terminal-declaring tool without its own keyed row (`terminal_send`) lost the
contract's above-card description. It now prefers the description exactly as
BashRow does.

A settled call read `call?.cwd`, which cannot tell "the call omitted a cwd"
from "the paging window dropped the call head". The second case has no cwd
anywhere and the original call may have used an explicit workdir, so it now
draws a bare `$` instead of naming the session workspace.

packages/client/ui-conversation/src/client/chat/GenericToolCard.tsx

@@ -28,6 +28,7 @@ const VARIANT_ICONS: Record<ToolRowVariant, ReactNode> = {
 
 export function GenericToolCard({ toolName, block, cwd, openFile }: ToolRowOwnerProps) {
   const model = toolRowModel(toolName, block, cwd)
+  const terminal = terminalCardModel(block, cwd)
   const singleFile = model.filePath !== undefined
   return (
     <ToolRow
@@ -35,10 +36,12 @@ export function GenericToolCard({ toolName, block, cwd, openFile }: ToolRowOwner
       toolName={toolName}
       icon={VARIANT_ICONS[model.variant]}
       title={model.title}
-      summary={model.summary}
+      // A terminal presenter's description is the contract's above-card text, so
+      // it outranks the args-derived summary here exactly as it does in BashRow.
+      summary={terminal?.description ?? model.summary}
       // Single-file tools never expose an args body — the path link is the only action.
       body={singleFile ? null : model.body}
-      terminal={terminalCardModel(block, cwd)}
+      terminal={terminal}
       state={model.state}
       filePath={model.filePath}
       onOpenFile={singleFile ? openFile : undefined}

packages/client/ui-conversation/src/client/contract/terminal-card-model.ts

@@ -68,31 +68,59 @@ function resolveTerminalCwd(viewCwd: string | undefined, sessionCwd: string | un
  * running, so a joined `/w/app/..` must display as `w`, not as `..`. Separators
  * are preserved as authored (a Windows path keeps its backslashes) because this
  * value is only ever displayed; a `..` that would climb past the root is
- * dropped, which is what a filesystem does with it.
+ * dropped, which is what a filesystem does with it. A UNC path's `server` and
+ * `share` are part of its root, not poppable segments: Windows cannot climb
+ * above a share, so `\\\\server\\share` with a `..` stays there.
  * @param path - a joined or absolute path, possibly carrying `.`/`..` segments.
  * @returns the same path with those segments resolved.
  */
 function normalizeSegments(path: string): string {
   if (!/(?:^|[/\\])\.\.?(?:[/\\]|$)/.test(path)) return path
+  // A UNC path is `\\\\server\\share\\...`: the server and share form the root,
+  // so they are split off here and neither is a segment `..` may pop. Its
+  // separator is fixed to a backslash, since a joined relative part may have
+  // introduced a forward slash that UNC syntax does not use.
+  const unc = /^[/\\]{2}([^/\\]+)[/\\]+([^/\\]+)/.exec(path)
+  if (unc !== null) {
+    // Both groups are mandatory in the pattern, so destructuring types them as
+    // strings without an assertion.
+    const [matched, server, share] = unc
+    const root = `\\\\${String(server)}\\${String(share)}`
+    // Rooted: what follows the share hangs off it, so a `..` at the top is
+    // dropped rather than kept — Windows cannot climb above a share.
+    const rest = collapse(path.slice(matched.length), true)
+    return rest === '' ? root : `${root}\\${rest}`
+  }
   const backslashed = path.includes('\\') && !path.includes('/')
   const separator = backslashed ? '\\' : '/'
-  const leading = /^[/\\]/.test(path) ? separator : ''
+  const rooted = /^[/\\]/.test(path)
   const drive = /^[A-Za-z]:/.exec(path)?.[0] ?? ''
+  const body = collapse(path.slice(drive.length), rooted || drive !== '', separator)
+  const leading = rooted ? separator : ''
+  return drive === '' ? `${leading}${body}` : `${drive}${rooted ? leading : separator}${body}`
+}
+
+/**
+ * Collapse the `.`/`..` segments of a path body against a known root state.
+ * @param body - the path after any drive letter or UNC root.
+ * @param rooted - the body hangs off a root, so a `..` at its top is dropped
+ *   the way a filesystem drops one; without a root the `..` is kept, since it
+ *   stays meaningful against a cwd this function cannot see.
+ * @param separator - separator to rejoin with (default `/`).
+ * @returns the collapsed body, without leading or trailing separators.
+ */
+function collapse(body: string, rooted: boolean, separator = '/'): string {
   const kept: string[] = []
-  for (const segment of path.slice(drive.length).split(/[/\\]/)) {
+  for (const segment of body.split(/[/\\]/)) {
     if (segment === '' || segment === '.') continue
     if (segment === '..') {
-      // Nothing to climb from: at a root the segment is dropped, matching the
-      // filesystem; on a relative path the `..` has to stay, since it is still
-      // meaningful against a cwd this function cannot see.
       if (kept.length > 0 && kept[kept.length - 1] !== '..') kept.pop()
-      else if (leading === '' && drive === '') kept.push(segment)
+      else if (!rooted) kept.push(segment)
       continue
     }
     kept.push(segment)
   }
-  const body = kept.join(separator)
-  return drive === '' ? `${leading}${body}` : `${drive}${leading === '' ? separator : leading}${body}`
+  return kept.join(separator)
 }
 
 /**
@@ -146,7 +174,12 @@ export function terminalCardModel(block: ToolCallBlock, sessionCwd?: string): Te
       // (the presentation contract's replacement-title rule); the call title is
       // what a result without one keeps.
       command: result.title ?? call?.title ?? '',
-      cwd: resolveTerminalCwd(call?.cwd, sessionCwd),
+      // Only a PRESENT call view can mean "omitted the cwd, so use the
+      // workspace". When the window dropped the call head there is no cwd
+      // anywhere — the result view carries none — and the original call may
+      // well have used an explicit workdir, so the prompt draws a bare `$`
+      // rather than naming a directory this card cannot know.
+      cwd: call === null ? undefined : resolveTerminalCwd(call.cwd, sessionCwd),
       output: result.output,
       exitCode: result.exitCode,
       signal: result.signal,

packages/client/ui-conversation/tests/terminal-card.spec.tsx

@@ -153,6 +153,32 @@ describe('terminalCardModel', () => {
     }))?.card.cwd).toBe('../elsewhere')
   })
 
+  it('keeps a UNC server and share as an unpoppable root', () => {
+    // Windows cannot climb above a share, so `..` from the share root stays put.
+    expect(terminalCardModel(settled({
+      callView: callTerminal({ cwd: '..' }),
+    }), '\\\\server\\share')?.card.cwd).toBe('\\\\server\\share')
+    // Below the share it pops normally, keeping the UNC separators.
+    expect(terminalCardModel(settled({
+      callView: callTerminal({ cwd: '..' }),
+    }), '\\\\server\\share\\app')?.card.cwd).toBe('\\\\server\\share')
+    // Several `..` cannot escape the root either.
+    expect(terminalCardModel(settled({
+      callView: callTerminal({ cwd: '../../..' }),
+    }), '\\\\server\\share\\app')?.card.cwd).toBe('\\\\server\\share')
+  })
+
+  it('draws a bare $ when the window dropped the call head, rather than guessing', () => {
+    // A truncated call carries no cwd anywhere: the result view has none, and
+    // the original call may have used an explicit workdir. Falling back to the
+    // session workspace here would name a directory the card cannot know.
+    expect(terminalCardModel(settled({
+      call: null, callView: null, resultView: resultTerminal({ title: 'ls -la' }),
+    }), '/w/app')?.card.cwd).toBeUndefined()
+    // A present call view that omits its cwd still means the workspace.
+    expect(terminalCardModel(settled(), '/w/app')?.card.cwd).toBe('/w/app')
+  })
+
   it('carries the call view\'s description, which the contract renders above the card', () => {
     expect(terminalCardModel(settled())?.description).toBe('List files')
     expect(terminalCardModel(running())?.description).toBe('List files')
@@ -231,6 +257,16 @@ describe('chat row terminal body', () => {
     expect(view.container.querySelectorAll('[data-terminal] [data-state]')).toHaveLength(1)
   })
 
+  it('the fallback row shows the presenter description, not the args summary', () => {
+    // Any terminal-declaring tool without its own keyed row lands here, so the
+    // contract's above-card description has to win at this render site as well.
+    const view = render(<GenericToolCard {...ownerProps(settled({
+      callView: callTerminal({ description: 'Terminal 3' }),
+    }))} />)
+    expect(view.getByText('Terminal 3')).toBeTruthy()
+    expect(view.queryByText('List files')).toBeNull()
+  })
+
   it('a running terminal call expands to the prompt line with no output yet', () => {
     const view = render(<GenericToolCard {...ownerProps(running())} />)
     fireEvent.click(view.container.querySelector('button')!)

packages/client/ui-primitives/src/ansi.ts

@@ -114,14 +114,49 @@ function applyCarriageReturns(text: string): string {
  */
 function applyBackspaces(text: string): string {
   if (!text.includes('\u0008')) return text
-  return text.split('\n').map((line) => {
-    const kept: string[] = []
-    for (const char of line) {
-      if (char === '\u0008') kept.pop()
-      else kept.push(char)
+  return text.split('\n').map(applyBackspacesToLine).join('\n')
+}
+
+/**
+ * One line's backspaces, resolved over VISIBLE characters only. A CSI sequence
+ * moves no cursor, so it must survive intact: erasing its bytes would corrupt
+ * the sequence and repaint the rest of the output with whatever the mangled
+ * remainder parses as. The sequences are therefore held as indivisible units
+ * that a backspace steps over on its way to the last printed character, and a
+ * unit already erased stays erased so a run's own color still applies to what
+ * remains of it.
+ * @param line - one output line, still carrying its CSI sequences.
+ * @returns the line with each backspace applied to the character before it.
+ */
+function applyBackspacesToLine(line: string): string {
+  if (!line.includes('\u0008')) return line
+  const units: { text: string; visible: boolean }[] = []
+  // Same shape anser splits on: CSI ... final byte. Matched here so a sequence
+  // is one unit rather than a run of erasable characters.
+  const csi = /\u001b\[[\u0030-\u003f]*[\u0020-\u002f]*[\u0040-\u007e]/g
+  let at = 0
+  for (const match of line.matchAll(csi)) {
+    for (const char of line.slice(at, match.index)) units.push({ text: char, visible: true })
+    units.push({ text: match[0], visible: false })
+    at = match.index + match[0].length
+  }
+  for (const char of line.slice(at)) units.push({ text: char, visible: true })
+
+  const kept: { text: string; visible: boolean }[] = []
+  for (const unit of units) {
+    if (unit.visible && unit.text === '\u0008') {
+      // Walk back past any escapes to the last printed character and drop it,
+      // keeping those escapes so the surviving text stays styled as authored.
+      for (let index = kept.length - 1; index >= 0; index--) {
+        if (kept[index]?.visible !== true) continue
+        kept.splice(index, 1)
+        break
+      }
+      continue
     }
-    return kept.join('')
-  }).join('\n')
+    kept.push(unit)
+  }
+  return kept.map(unit => unit.text).join('')
 }
 
 /**

packages/client/ui-primitives/tests/ansi.spec.ts

@@ -184,6 +184,24 @@ describe('parseAnsiLines: backspaces', () => {
     ])
   })
 
+  it('steps over an SGR sequence instead of erasing its bytes', () => {
+    // `abc` reset then two backspaces then `XY`: erasing the reset's bytes would
+    // corrupt it and repaint the rest of the line with whatever the remainder
+    // parses as. The visible result is `aXY`, still red, with the reset intact.
+    expect(parseAnsiLines(`${sgr('31', 'abc')}${BS}${BS}XY`)).toEqual([[
+      { text: 'a', style: { color: 'var(--dsw-alias-state-error-primary)' } },
+      { text: 'XY', style: undefined },
+    ]])
+  })
+
+  it('erases across a style boundary without dropping the styles between', () => {
+    // The backspace reaches back past the reset to the last printed character.
+    expect(parseAnsiLines(`${sgr('32', 'ok')}${ESC}[31m${BS}bad`)).toEqual([[
+      { text: 'o', style: { color: 'var(--dsw-alias-state-success-primary)' } },
+      { text: 'bad', style: { color: 'var(--dsw-alias-state-error-primary)' } },
+    ]])
+  })
+
   it('applies the overwrite after a carriage-return redraw, not before', () => {
     // The redraw wins first; the backspace then erases inside what survived.
     expect(onlySpan(`old\rnew${BS}`)).toEqual({ text: 'ne', style: undefined })