fix(hopper): verify and repair the Linux embedding runtime (#5041)

Verify the distribution Python embedding library during approved Linux Hopper
setup, conditionally repair the matching Ubuntu dependency, and confirm that
the library loads. Share fresh bounded observations with doctor, preserve
unknown configuration and caller cancellation, and join probe exit through
the existing process supervisor.

Validate clean Ubuntu installation, normal-user real Hopper CLI/MCP workflows,
independent ELF/SQLite oracles, cancellation and cleanup regressions, 154
focused checks and all 40 current-head CI checks. Preserve measured artifact
identity, failed attempts and local host-memory guard limitations.

Closes #5015.

Co-authored-by: Kaoru0822 <208281322+kaoru0822-kitauji@users.noreply.github.com>

docs/installation.md

@@ -599,6 +599,20 @@ host mount and the rest of `/tmp` remain unchanged; this fallback never invokes
 `sudo`. `rea doctor --provider hopper --json` reports the selected
 strategy and both host and effective mount facts.
 
+Hopper also embeds Python; the Python executable and standard library alone
+are insufficient on Ubuntu. Approved setup checks the system interpreter
+at `/usr/bin/python3` and, when necessary, installs its matching
+`libpython3.X` package, then verifies that its shared library can load.
+APT resolves the concrete package (for example, `libpython3.12t64` on Ubuntu
+24.04). Doctor includes these fresh observations in the `embedded_python`
+details of its `hopper-demo-runtime` check, alongside the private-display
+diagnostic. Failed inspections remain unknown rather than proving a library
+absent. Run `rea setup --yes --install-hopper` to repair a supported install.
+This prerequisite check does not launch the bridge or validate a custom Python
+interpreter configured inside Hopper; that interpreter needs its own matching
+shared runtime. Custom installation prefixes or shared-library ABIs require
+manual dependency repair.
+
 When the package-manager step fails, setup reports the failing command and its
 captured output, so a package conflict is distinguishable from an authorization
 failure. On CachyOS, an unversioned compatibility package such as