feat(react): React introspection, Web Vitals, and SPA primitives (#1257)

* feat(react): first-class React introspection, Web Vitals, and nextjs skill

Add React-general and web-universal features as first-class agent-browser verbs
(react tree/inspect/renders/suspense, vitals, pushstate). Genuinely Next.js-specific
workflows (PPR cookie protocol, /_next/mcp bridge, dev-server endpoints) ship as
a new `nextjs` skill that composes the primitives. No new runtime dependencies -
the React DevTools installHook.js is vendored (MIT) and include_str!'d into the
binary.

New commands:
  react tree                  Full React component tree (depth id parent name)
  react inspect <fiberId>     Props, hooks, state, source for one fiber
  react renders start|stop    Fiber profiler with Insts/Mounts/Re-renders/Self/DOM
                              + prev->next change details
  react suspense              Suspense boundaries + classifier (client-hook,
                              request-api, server-fetch, cache, stream, framework)
                              + root-cause grouping + recommendations
  vitals [url]                LCP/CLS/TTFB/FCP/INP + React hydration phases
  pushstate <url>             Generic SPA client-side navigation
  removeinitscript <id>       Remove a script registered via addinitscript

New launch flags:
  --init-script <path>        Register init scripts before first navigation
                              (repeatable; env AGENT_BROWSER_INIT_SCRIPTS)
  --enable <feature>          Built-in init scripts; currently react-devtools
                              (repeatable; env AGENT_BROWSER_ENABLE)

Other primitives:
  network route ... --resource-type <csv>  Filter by CDP resource type
  cookies set --curl <file>                Auto-detects JSON/cURL/Cookie-header

* fixes

* fixes

* fixes

skill-data/core/references/commands.md

@@ -5,16 +5,38 @@ Complete reference for all agent-browser commands. For quick start and common pa
 ## Navigation
 
 ```bash
-agent-browser open <url>      # Navigate to URL (aliases: goto, navigate)
+agent-browser open            # Launch browser (no navigation); stays on about:blank.
+                              # Pair with `network route`, `cookies set --curl`, or
+                              # `addinitscript` to stage state before the first navigation.
+agent-browser open <url>      # Launch + navigate (aliases: goto, navigate)
                               # Supports: https://, http://, file://, about:, data://
                               # Auto-prepends https:// if no protocol given
 agent-browser back            # Go back
 agent-browser forward         # Go forward
 agent-browser reload          # Reload page
+agent-browser pushstate <url> # SPA client-side navigation. Auto-detects
+                              # window.next.router.push (triggers RSC fetch on Next.js);
+                              # falls back to history.pushState + popstate/navigate events.
 agent-browser close           # Close browser (aliases: quit, exit)
 agent-browser connect 9222    # Connect to browser via CDP port
 ```
 
+### Pre-navigation setup (one-turn batch)
+
+```bash
+agent-browser batch \
+  '["open"]' \
+  '["network","route","*","--abort","--resource-type","script"]' \
+  '["cookies","set","--curl","cookies.curl","--domain","localhost"]' \
+  '["navigate","http://localhost:3000/target"]'
+```
+
+`open` with no URL gives you a clean launch so any interception, cookies,
+or init scripts you register take effect on the *first* real navigation.
+Use for SSR-only debug (`--resource-type script`), protected-origin auth,
+or capturing fresh `react suspense`/`vitals` state without noise from a
+prior page.
+
 ## Snapshot (page analysis)
 
 ```bash
@@ -310,12 +332,57 @@ agent-browser profiler start              # Start Chrome DevTools profiling
 agent-browser profiler stop trace.json    # Stop and save profile
 ```
 
+## React / Web Vitals
+
+Requires `--enable react-devtools` at launch for the `react ...` commands.
+`vitals` and `pushstate` are framework-agnostic.
+
+```bash
+agent-browser open --enable react-devtools <url>    # Launch with React hook installed
+agent-browser react tree                            # Full component tree
+agent-browser react inspect <fiberId>               # Props, hooks, state, source
+agent-browser react renders start                   # Begin re-render recording
+agent-browser react renders stop [--json]           # Stop and print render profile
+agent-browser react suspense [--only-dynamic] [--json]  # Suspense boundaries + classifier
+                                                         # --only-dynamic hides the "static" list
+agent-browser vitals [url] [--json]                 # LCP/CLS/TTFB/FCP/INP + hydration
+agent-browser pushstate <url>                       # SPA client-side nav (auto-detects Next router)
+```
+
+## Init scripts
+
+```bash
+agent-browser open --init-script <path>             # Register before first navigation (repeatable)
+agent-browser addinitscript <js>                    # Register at runtime (returns identifier)
+agent-browser removeinitscript <identifier>         # Remove a previously registered init script
+```
+
+## cURL cookie import
+
+```bash
+agent-browser cookies set --curl <file>                             # Auto-detects JSON/cURL/Cookie-header
+agent-browser cookies set --curl <file> --domain example.com        # Scope to a domain
+```
+
+Supported formats: JSON array of `{name, value}`, a cURL dump from
+DevTools -> Network -> Copy as cURL, or a bare Cookie header. Errors never
+echo cookie values.
+
+## Network route by resource type
+
+```bash
+agent-browser network route '*' --abort --resource-type script       # Block scripts only (SSR-lock pattern)
+agent-browser network route '*' --resource-type image,font --body '' # Stub images and fonts
+```
+
 ## Environment Variables
 
 ```bash
 AGENT_BROWSER_SESSION="mysession"            # Default session name
 AGENT_BROWSER_EXECUTABLE_PATH="/path/chrome" # Custom browser path
 AGENT_BROWSER_EXTENSIONS="/ext1,/ext2"       # Comma-separated extension paths
+AGENT_BROWSER_INIT_SCRIPTS="/a.js,/b.js"     # Comma-separated init script paths
+AGENT_BROWSER_ENABLE="react-devtools"        # Comma-separated built-in init script features
 AGENT_BROWSER_PROVIDER="browserbase"         # Cloud browser provider
 AGENT_BROWSER_STREAM_PORT="9223"             # Override WebSocket streaming port (default: OS-assigned)
 AGENT_BROWSER_HOME="/path/to/agent-browser"  # Custom install location