[jdupak]

Replaces the Python implementation with a single Rust binary. Three commits:

• Rewrite ShellGame in Rust: the port.
• Remove the Python implementation.
• Restructure the Rust engine and fix the review findings:
  • levels become const struct literals, one file per section;
  • positions ("S.L") replace ids, with state.json v3;
  • the game shell is confined by Landlock;
  • the docs move into AGENTS.md, module docs and skills;
  • a deep review's fixes.

What changes for students

• Re-install: students on the Python build (build-13) have no shellgame update; they need to re-run the installer once. install.sh is now POSIX sh, and its overrides are renamed to SHELLGAME_INSTALL_DIR and SHELLGAME_REPO.
• Old saves: a Python save is set aside as state-old.json and a new game starts. The notice names the command to continue, e.g. shellgame resume 5.3. A save from a newer version is refused, with a hint to run shellgame update.
• Landlock or --unsafe: the game shell can change files only in /tmp, the state directory and /dev. Without Landlock (e.g. macOS, WSL 1, old kernels) the game refuses to start unless run with --unsafe.
• Same course: the 12 sections are the same as in the Python version, with grading, wording and Czech fixes from the review. Answers that were only labels are now a bare shellgame submit. New CLI: hint -r, plus levels, resume, update and --version.

Review fixes in the last commit

• reset rescue: it repairs a damaged workspace or section directory (lost permissions, a file or a symlink in its place, never followed). A parent directory without x no longer reads as "your directory was deleted".
• Level bugs:
  • 2.7: the text gave the answer away.
  • 2.2: the cd - drill counted from anywhere.
  • 9.8: the mistake message for 3 was wrong.
  • 9.10: the Ctrl+C claims were false.
  • 11.4–11.6: find . paths, quoting and the format example.
  • Section 7: a move was accepted where the task says copy.
  • Section 6: the alias sg collided with /usr/bin/sg.
  • Also fixed: the Linux ~ keyboard help and both ls -l diagrams.
• CI:
  • publishes only a commit that is still the tip of main, so an older build can't become latest;
  • the bash 3.2 shell tests on macOS now block a release;
  • the static Linux binary is smoke-tested in a confined game shell;
  • docs deploy only after CI succeeds.
• Tests:
  • new cases for the reset damage, save versions, hint -r and a parent without x;
  • replays fail on a missing command;
  • Landlock ABI and over-restriction steps;
  • no pinned Czech wording;
  • the course validation also scans failed-check messages for leaked answers.

Before merging

• Conflicts with main: it has a69c0a4 (feat: add levels and resume commands #2, levels and resume for the Python version). This branch replaces those files, so the conflicts should resolve in favour of this branch.
• CI on GitHub: the workflow changes (publish guard, macOS blocking step, smoke test, workflow_run docs deploy) have only run locally. Check this PR's run. Whether the arm64 runner has Landlock is unknown; without it the smoke test falls back to --unsafe with a warning.
• Maintainer decisions:
  • 4.1 duplicates 2.6; removing it would shift saved positions.
  • 5.2 is no longer optional.
  • 1.11 doesn't enforce running pwd before the final cd.
  • submit joins its words with spaces.
  • Content checks are exact, so a missing final newline is rejected; the messages now say so.
• macOS content review (assets stay held back by PUBLISH_MACOS).

Test plan

Run locally on Linux with Landlock:

• cargo fmt --check, cargo clippy --all-targets --locked -- -D warnings, RUSTDOCFLAGS="-D warnings" cargo doc --no-deps: clean.
• SHELLGAME_TEST_LANDLOCK=required cargo test --locked:
  • unit and validation: 42
  • cli: 22
  • e2e: 195 (every solution in bash and fish, playthroughs, strict cd, regressions)
  • sandbox: 3
  • shell: 22
  • doctest: 1
• shellcheck: every tracked *.sh passes.
• By hand: reset after each damage case, old/new saves, hint -r, repeat, and 2.2, 3.4, 6.7 and 11.5 in tmux.

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