Support session

[kerthcet]

What this PR does / why we need it

Which issue(s) this PR fixes

Fixes #

Special notes for your reviewer

Does this PR introduce a user-facing change?

[Copilot]

Pull request overview

This PR implements first-class interactive PTY sessions end-to-end (daemon ⇄ server ⇄ Python), renaming the previous “shell” concept to “session” across the protocol, Rust code, Python bindings, tests, and docs.

Changes:

• Replaced Shell* protocol/messages and APIs with Session* equivalents, including a new SessionClose message.
• Implemented PTY-backed session management in the daemon and exposed a Python Session handle with write/read/resize/close (+ optional interactive terminal mode).
• Updated examples, docs, and tests to use server.exec() and server.new_session().

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
server/src/server.rs	Forwards SessionOutput/SessionExit from daemon to Python-side session streams.
server/src/registry.rs	Renames shell session routing map to sessions and updates routing methods.
server/src/protocol.rs	Renames shell message variants to session variants and adds SessionClose. Updates protocol tests accordingly.
server/src/lib.rs	Renames Python binding execute_command→exec, start_shell→new_session; introduces Session pyclass and adds close().
sandd/src/session.rs	Adds daemon-side PTY session implementation (start/read/write/resize/close).
sandd/src/protocol.rs	Mirrors protocol rename from shell messages to session messages.
sandd/src/main.rs	Wires SessionManager into daemon message handling for start/input/resize/close.
README.md	Updates project messaging and example code to exec() and “Interactive Sessions”.
python/tests/test_unit.py	Updates unit tests to use exec() and new_session().
python/tests/test_integration.py	Updates integration tests to exec(); comments out file-transfer tests.
python/tests/test_e2e.py	Updates to exec() and adds E2E coverage for interactive sessions.
python/sandd/init.py	Updates Python wrapper API (exec, new_session) and adds interactive terminal loop.
pyproject.toml	Updates package description string.
Makefile	Renames docker helper target (docker-up) and removes test-all.
examples/interactive_session.py	New interactive session example script.
examples/install_htop.py	Updates to exec() and adjusts guidance for interactive usage.
examples/exec_commands.py	Updates to exec() and refreshes script description.
examples/agent_example.py	Removes legacy example script.
docs/QUICKSTART.md	Updates docs snippets from execute_command() to exec() and shell→session.
docs/PROTOCOL.md	Updates protocol documentation to session terminology and adds SessionClose.
docs/DEVELOP.md	Updates developer docs to reference session implementation and new API names.
docs/ARCHITECTURE.md	Updates terminology from shell output to session output.
.github/workflows/rust-ci.yaml	Removes E2E tests from CI, leaving make test only.

Comments suppressed due to low confidence (4)

sandd/src/session.rs:7

• reader.read(&mut buffer) relies on the std::io::Read trait, but only Write is imported. This will fail to compile unless the reader type provides an inherent read() (portable-pty readers typically implement Read).
  sandd/src/session.rs:199
• close_session() removes the handle but never stops the spawned reader task. Dropping the JoinHandle does not cancel it, so the task can continue reading/sending after a session is “closed”. Abort the task when closing the session.
  sandd/src/session.rs:100
• The PTY reader loop performs a blocking std::io::Read::read() inside tokio::spawn. This can block a Tokio worker thread per active session (and send_input()/resize() also perform blocking Write/resize calls under async locks), which can degrade throughput or stall other async tasks under load. Consider moving PTY I/O to spawn_blocking/dedicated threads and forwarding data over async channels.
  python/sandd/init.py:160
• Renaming execute_command() → exec() (and start_shell() → new_session()) is a breaking change for existing Python consumers. If backward compatibility matters, consider keeping the old method names as thin wrappers (deprecated) for at least one release, or bumping the major version and calling this out in release notes/docs.

    def exec(
        self,
        daemon_id: str,
        command: str,
        timeout: int = 300,
        env: Optional[Dict[str, str]] = None,
        cwd: Optional[str] = None,
    ) -> CommandResult:

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