Stop Playwright setup from deleting the package it just installed

Setting up the browser view failed on every container, and re-running it
reproduced the same broken state, because the setup destroyed its own work.

`install_packages` ran two `npm install --no-save` commands into
/workspace, which has no package.json. With no manifest, npm treats the
command line as the whole statement of what the tree should contain and
prunes the rest, so installing `playwright` second removed the
`@playwright/cli` installed first: "removed 3 packages", leaving an empty
node_modules/@playwright/ behind playwright and playwright-core. That
empty directory is exactly what the pane then reported as missing. The
second install now names both specs; the first one is already present, so
it costs nothing and is only there to stop npm pruning it.

Two failures were waiting behind that one:

Nothing in the tree ever configured the browser, so playwright-cli fell
back to channel `chrome` — system Google Chrome — with the Chromium
sandbox on. These containers forbid unprivileged user namespaces, so it
aborted with "Failed to move to new namespace ... Operation not
permitted"; on a base image without Google Chrome the same default failed
as "Chromium distribution 'chrome' is not found". entrypoint.sh now seeds
~/.playwright/cli.config.json on every start, which is the only way to
reach existing projects: ~/.playwright is inside the home volume, so an
image copy would reach new projects only.

The launch check passed for a configuration the viewer never uses. It
launched bundled chromium with no channel, which resolves to
chromium-headless-shell, while the viewer's config pins
chrome-for-testing — the full chromium build, a separate download. A
container could pass every check and still fail in the pane with 'Browser
"chrome-for-testing" is not installed', which is what a stale
chromium-1217 against a wanted chromium-1237 did. Chromium is now
verified on both channels, the sandbox setting is stated rather than
inherited from a default, and a failure names the channel.

triple-c-playwright-heal repairs all of it on a container that is already
broken, including the missing socat that makes the pane report
"127.0.0.1 sent an invalid response" while the container side is
perfectly healthy. It verifies by launching a browser rather than
trusting the preceding steps — which is how the stale-revision case was
found — and lives in /usr/local/bin so a fix to it can still reach an
existing project.

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

container/Dockerfile

@@ -318,6 +318,13 @@ COPY entrypoint.sh /usr/local/bin/entrypoint.sh
 RUN chmod +x /usr/local/bin/entrypoint.sh
 COPY triple-c-scheduler /usr/local/bin/triple-c-scheduler
 RUN chmod +x /usr/local/bin/triple-c-scheduler
+# Lives in /usr/local/bin rather than under /home/claude on purpose: the home
+# directory is the mount point of the project's home volume, so an image copy
+# of it is masked after the project's first start and can never be updated
+# again. /usr/local/bin rides the snapshot and is replaced on migration, which
+# is what lets a fix to this script reach an existing project at all.
+COPY triple-c-playwright-heal /usr/local/bin/triple-c-playwright-heal
+RUN chmod +x /usr/local/bin/triple-c-playwright-heal
 COPY triple-c-task-runner /usr/local/bin/triple-c-task-runner
 RUN chmod +x /usr/local/bin/triple-c-task-runner