batch3 T8: chat->file click, Session.tsx rewires to Workspace, sidebar polish

- MessageBubble & ToolCallCard: detect path-like strings in rendered text
  via regex requiring slash+extension; clicks dispatch open_file_in_browser
- Session.tsx: now renders <Workspace sessionId projectId>; on mount,
  emits session_loaded so sidebar can highlight even deep-linked sessions
  not in the recent_sessions cache
- ProjectSidebar: active project's chevron visually disabled (50% opacity,
  cursor-not-allowed) and click no-op; activeSession from useSidebar used
  as fallback when active session isn't in cache

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/components/MessageBubble.tsx

@@ -1,13 +1,86 @@
-import { useState } from 'react';
+import { Children, cloneElement, isValidElement, useState } from 'react';
+import type { ReactElement, ReactNode } from 'react';
 import Markdown from 'react-markdown';
 import remarkGfm from 'remark-gfm';
 import { Copy, RefreshCw, Check } from 'lucide-react';
 import { toast } from 'sonner';
 import type { Message } from '@/api/types';
 import { api } from '@/api/client';
+import { sessionEvents } from '@/hooks/sessionEvents';
 import { ToolCallCard } from './ToolCallCard';
 import { CodeBlock } from './CodeBlock';
 
+// Match path-shaped substrings ending in `.ext`. Additionally require a `/`
+// in the match to reduce false positives in prose (e.g. plain `foo.ts` won't
+// match, but `src/foo.ts` will). False positives at the edges are accepted
+// per Sam's design decision (2026-05-14).
+const PATH_REGEX = /([a-zA-Z0-9._/-]+\.[a-zA-Z0-9]+)/g;
+
+function isPathLike(s: string): boolean {
+  return s.includes('/');
+}
+
+function emitOpenFile(path: string): void {
+  sessionEvents.emit({ type: 'open_file_in_browser', path });
+}
+
+// Split a plain string into a flat array of strings and clickable button
+// nodes for path-shaped substrings. If no matches, returns the original
+// string verbatim (no array wrapping).
+function linkifyPaths(text: string, keyPrefix: string): ReactNode {
+  const out: ReactNode[] = [];
+  let lastIdx = 0;
+  let idx = 0;
+  for (const match of text.matchAll(PATH_REGEX)) {
+    const matchedText = match[0];
+    const start = match.index ?? 0;
+    if (!isPathLike(matchedText)) continue;
+    if (start > lastIdx) out.push(text.slice(lastIdx, start));
+    out.push(
+      <button
+        key={`${keyPrefix}-${idx}`}
+        type="button"
+        onClick={() => emitOpenFile(matchedText)}
+        className="text-primary underline cursor-pointer hover:text-primary/80"
+      >
+        {matchedText}
+      </button>
+    );
+    lastIdx = start + matchedText.length;
+    idx += 1;
+  }
+  if (out.length === 0) return text;
+  if (lastIdx < text.length) out.push(text.slice(lastIdx));
+  return out;
+}
+
+// Walk react-markdown children, linkifying string text nodes. Children of
+// <code> nodes (CodeBlock and inline code) are left untouched — the regex
+// shouldn't run inside code spans.
+function linkifyChildren(children: ReactNode, keyPrefix = 'l'): ReactNode {
+  const arr = Children.toArray(children);
+  return arr.map((child, i) => {
+    if (typeof child === 'string') {
+      return (
+        <span key={`${keyPrefix}-${i}`}>
+          {linkifyPaths(child, `${keyPrefix}-${i}`)}
+        </span>
+      );
+    }
+    if (isValidElement(child)) {
+      const el = child as ReactElement<{ children?: ReactNode }>;
+      // Skip inline/block code — paths in code spans aren't link targets.
+      if (el.type === 'code' || el.type === CodeBlock) return child;
+      const grandchildren = el.props.children;
+      if (grandchildren === undefined) return child;
+      return cloneElement(el, {
+        children: linkifyChildren(grandchildren, `${keyPrefix}-${i}`),
+      });
+    }
+    return child;
+  });
+}
+
 interface Props {
   message: Message;
   sessionId: string;
@@ -55,7 +128,10 @@ function MarkdownBody({ content }: { content: string }) {
         ol: ({ children }) => (
           <ol className="list-decimal pl-5 space-y-1">{children}</ol>
         ),
-        p: ({ children }) => <p className="leading-relaxed">{children}</p>,
+        li: ({ children }) => <li>{linkifyChildren(children)}</li>,
+        p: ({ children }) => (
+          <p className="leading-relaxed">{linkifyChildren(children)}</p>
+        ),
         h1: ({ children }) => <h1 className="text-base font-semibold mt-2">{children}</h1>,
         h2: ({ children }) => <h2 className="text-sm font-semibold mt-2">{children}</h2>,
         h3: ({ children }) => <h3 className="text-sm font-semibold mt-1">{children}</h3>,
@@ -73,7 +149,9 @@ function MarkdownBody({ content }: { content: string }) {
           <th className="border border-border px-2 py-1 text-left font-medium">{children}</th>
         ),
         td: ({ children }) => (
-          <td className="border border-border px-2 py-1">{children}</td>
+          <td className="border border-border px-2 py-1">
+            {linkifyChildren(children)}
+          </td>
         ),
       }}
     >