Install one Playwright tree, and notice when a container has two

Setup installed `playwright@latest` and `@playwright/cli@latest` together.
Verified on a real container, that produces a tree that looks right and is
broken: `@playwright/cli@0.1.18` pins `playwright-core@1.63.0-alpha`, npm
hoists it, and `playwright@latest` (1.62.1) nests its own
`playwright-core@1.62.1` beside it. The two cores want different browser
revisions.

The browser step runs the *resolved* — hoisted — CLI, so it downloads
chromium-1237. Every script Claude writes says `require("playwright")`,
gets the nested 1.62.1, and dies with:

  Executable doesn't exist at …/chromium_headless_shell-1234/…

while the pane reports a browser installed, because one is. This is
deterministic, not bad luck: every container set up through the pane
lands in it.

So the viewer package is installed first, and the `playwright` version
installed after it is the one that package pins — read from the manifest
npm just wrote, falling back to `@latest` only if it cannot be read. One
core, one browser revision, both halves agreeing. Re-running "Set up
Playwright" repairs an already-split tree.

Detection now asks the question directly rather than listing a cache: it
asks each resolved copy for `chromium.executablePath()` and whether that
file exists — the viewer's copy *and* the one `require("playwright")`
returns, since those are routinely different. `needs_browser()` covers
"installed but not launchable", and the pane names both halves instead of
saying "install a browser" over a cache that visibly has one.

An absent field is "the probe didn't answer", never "skewed": containers
predating these fields must not be told their browsers are wrong. The
Rust side gets that from Option; the TypeScript mirror needed `!= null`,
which an existing test caught.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/lib/types.ts

@@ -469,6 +469,15 @@ export interface PlaywrightDetection {
   /** Path to Google Chrome when the `chrome` channel — what `@playwright/mcp`
    *  asks for — is installed. It is an apt package, so it is never in `browsers`. */
   chrome_channel: string | null;
+  /** The Chromium the *viewer's* Playwright would launch, and whether it exists. */
+  chromium_executable: string | null;
+  chromium_executable_exists: boolean;
+  /** What a script's `require("playwright")` resolves to — routinely a different
+   *  copy, pinning a different browser revision. If its Chromium is missing,
+   *  every script Claude writes fails while the pane still looks green. */
+  script_playwright_version: string | null;
+  script_chromium_executable: string | null;
+  script_chromium_executable_exists: boolean;
   /** Module roots the probe searched, echoed back for the "not found" message.
    *  Includes the npx cache (`~/.npm/_npx/*​/node_modules`), which is where a
    *  Playwright installed through Claude Code's MCP setup actually lives. */