🤖 v1.0.218: Claude Code 2.1.265 installer reports success but leaves no launcher on ubuntu-latest, every run fails with "native binary not found"

## Summary

Since v1.0.218 (commit 0d0e087, "bump Claude Code to 2.1.265 and Agent SDK to 0.3.265", tagged `v1` at 2026-09-08 20:39 UTC) every run of the action on `ubuntu-latest` fails before Claude starts:

```
SDK execution error: ReferenceError: Claude Code native binary not found at /home/runner/.local/bin/claude. Please ensure Claude Code is installed via native installer or specify a valid path with options.pathToClaudeCodeExecutable.
telemetryMessage: "Claude Code native binary not found at the configured path (ENOENT)",
errorClass: "executable_not_found",
```

The install step (`curl -fsSL https://claude.ai/install.sh | bash -s -- 2.1.265`) exits 0 and prints "successfully installed" / "Installation complete!", but the 2.1.265 binary's `claude install` never creates the launcher. Its own setup notes say so, twice:

```
Installing Claude Code native build 2.1.265...
Setting up launcher and shell integration...
⚠ Setup notes:
● claude command at /home/runner/.local/bin/claude missing or broken (/home/runner/.local/bin does not exist)
● claude command at /home/runner/.local/bin/claude missing or broken

✔ Claude Code successfully installed!

Version: 2.1.265

Location: ~/.local/bin/claude
```

Because the installer reports success, the retry loop in `installClaudeCode()` never triggers and the action goes on to spawn a path that does not exist.

## Runs

- Failing (v1.0.218, Claude Code 2.1.265): https://github.com/episode6/collins/actions/runs/34285384330 — reran it once, identical failure at the same step.
- Passing earlier the same day on the same image (v1.0.217, Claude Code 2.1.263): https://github.com/episode6/collins/actions/runs/34179464399 — "Setting up launcher and shell integration..." is followed directly by "✔ Claude Code successfully installed!" with no setup notes, and the launcher exists.

The workflow is the stock `issue_comment` / `@claude` tag-mode workflow with `claude_code_oauth_token` and `additional_permissions: actions: read`, nothing else: https://github.com/episode6/collins/blob/main/.github/workflows/claude.yml

## What I could and could not reproduce

- The same install command for 2.1.265 in a fresh `$HOME` on a Linux desktop (no `~/.local` at all) succeeds and creates the `~/.local/bin/claude` symlink, also with `CI=true GITHUB_ACTIONS=true` set and with a nonexistent `$HOME/.local/bin` on `PATH` the way the runner images have it. So it is not a generic installer bug; something on the hosted runner makes the 2.1.265 launcher step fail silently.
- Only the pinned version changed between v1.0.217 and v1.0.218 (`src/entrypoints/run.ts` line 80).

## Workarounds

- Pin the action to v1.0.217 (`anthropics/claude-code-action@9c5ddab2e6d17b83ea679153b31f1d5f023cf636`).
- Or install Claude Code in a previous step and pass `path_to_claude_code_executable`.

## Suggestions

- Verify the executable exists (and runs `--version`) after the install step, so "installed successfully" cannot be printed over a missing launcher and the retry/failure surfaces at the right place.
- The 2.1.265 native installer reporting success while its own diagnostics say the launcher is missing looks like a Claude Code bug; happy to file it there too if you can point at what the launcher step does differently on hosted runners.