[Sadykhzadeh]

Closes #147. Stacked on #140 (session.rs). Merge #140 first; this PR's base then becomes main.

What this changes

Server-initiated channels are refused

SshHandler now overrides every server_channel_open_* hook russh 0.63.3 offers and rejects each one with AdministrativelyProhibited:

• agent forward
• X11
• forwarded-tcpip, forwarded-streamlocal
• direct-tcpip, direct-streamlocal
• session

Unknown channel types were already refused, since russh's should_accept_unknown_server_channel defaults to false. Clavyn requests no forwarding of any kind, so no legitimate flow is affected. If agent forwarding is added later, it has to opt back in here, deliberately.

The startup command is typed into the shell

A session channel takes one of shell, exec or subsystem. OpenSSH ignores an exec that arrives after the shell, so startup_command never ran. It is now written into the shell followed by \r, the bytes Enter sends, which matches what "startup command" means in a terminal client: the shell starts and the command runs in it.

Tests

core/tests/server_requests.rs runs against an in-process russh server.

• channels_the_server_opens_back_are_refused: once the shell starts, the server tries to open agent, x11, forwarded-tcpip and session channels, and each open must fail.
• the_startup_command_is_typed_into_the_shell: the server must receive exactly tmux attach\r on the shell channel.

Both fail on the base branch and pass here.

Test plan

• cargo test -p clavyn-core: all suites pass (118 + 5 + 32 + 2 + 3 + 9)
• node scripts/verify/check-comments.mjs: ok
• CI

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[qodo-code-review]

PR Summary by Qodo

Reject server-initiated SSH channels and run startup commands in the shell

🐞 Bug fix 🧪 Tests 🕐 20-40 Minutes

AI Description

• Reject server-initiated SSH channels to prevent unused channels accumulating on client
 connections.
• Type startup commands into the interactive shell so they run after the shell starts.
• Add loopback-server tests for channel refusal and exact startup-command bytes.

Diagram

sequenceDiagram
    participant Manager as Session Manager
    participant Server as SSH Server
    participant Handler as SSH Handler
    participant Shell as Remote Shell
    Manager->>Server: Request PTY and shell
    Server->>Shell: Start shell
    Server->>Handler: Open channel back
    Handler-->>Server: Reject channel
    Manager->>Server: Send startup command + CR
    Server->>Shell: Deliver input

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High-Level Assessment

The approach fits an interactive terminal client: refuse unsolicited channels at russh's handler boundary and send the startup command through the existing shell. An exec request would not run after shell startup, while a separate exec channel would not run inside that shell.

Files changed (3) +288 / -4

Bug fix (2) +97 / -4

connection.rsRefuse all known server-initiated channel types +91/-1

Refuse all known server-initiated channel types

• SshHandler overrides seven russh channel-open hooks and rejects each request as AdministrativelyProhibited. A shared helper keeps the rejection behavior consistent.

core/src/connection.rs

session.rsSend startup commands as shell input +6/-3

Send startup commands as shell input

• After requesting the shell, SessionManager writes a configured startup command followed by a carriage return instead of issuing an exec request on the same channel.

core/src/session.rs

Tests (1) +191 / -0

server_requests.rsTest reverse-channel refusal and startup input +191/-0

Test reverse-channel refusal and startup input

• Adds an in-process russh server that checks refusal of agent, X11, forwarded-TCP and session channels. A second test verifies that the shell receives exactly 'tmux attach\r'; the other three overridden channel types are not exercised here.

core/tests/server_requests.rs

[qodo-code-review]

Code Review by Qodo