feat(cli): add minimal ao send

[harshitsinghbhandari]

Summary

Adds the minimal ao send path for sending a message to a running session through the existing daemon API.

ao send --session <id> --message "..." now:

1. validates required CLI flags
2. POSTs { "message": "..." } to /api/v1/sessions/{id}/send
3. resolves the session runtime handle from sqlite
4. calls the existing zellij SendMessage, which pastes the message into the agent pane and presses Enter

Intentionally not included:

• durable .ao/inbox files
• composite messenger fanout
• pane-ping pointer messages
• new runtime WriteChars seam

Closes #79.

Test plan

• go test ./internal/cli ./internal/daemon ./internal/session_manager ./internal/httpd/controllers

Focused tests cover CLI success/validation/error handling, preserving message whitespace, daemon messenger runtime-handle lookup, and sentinel error wrapping for HTTP error mapping.

[greptile-apps]

Greptile Summary

This PR wires the ao send CLI path end-to-end: a new send subcommand in cli/send.go POSTs to the existing /api/v1/sessions/{id}/send HTTP endpoint, which then flows through the session service and a new runtimeMessenger adapter that replaces the previous noopMessenger stub to actually paste the message into the live zellij pane.

• CLI (send.go): validates --session and --message, preserves message whitespace intentionally (tested), and URL-path-escapes the session ID before calling postJSON.
• Daemon wiring (lifecycle_wiring.go): removes noopMessenger, adds runtimeMessenger which resolves the RuntimeHandleID from the store, checks IsTerminated, and delegates to runtime.SendMessage; sentinel errors (ErrNotFound, ErrTerminated, ErrIncompleteHandle) are wrapped for writeSessionError to map to appropriate HTTP status codes.
• HTTP controller (sessions.go): adds a ErrTerminated → 409 SESSION_TERMINATED case to writeSessionError to complete the error-mapping table for the send path.

Confidence Score: 5/5

Safe to merge; the change is a self-contained, well-tested addition with no modifications to existing logic paths.

The new messenger replaces a no-op stub with a straightforward store-lookup-then-runtime-call, all sentinel errors are properly chained for existing HTTP error mapping, CLI validation is correct and covered by tests, and the daemon wiring is additive. No existing behavior is altered.

No files require special attention.

Important Files Changed

Filename	Overview
backend/internal/cli/send.go	New ao send command; validates flags, preserves message whitespace, URL-escapes session ID, delegates to existing postJSON.
backend/internal/daemon/lifecycle_wiring.go	Replaces noopMessenger with runtimeMessenger; correctly handles not-found, terminated, and incomplete-handle sentinel errors via errors.Is-compatible wrapping.
backend/internal/daemon/wiring_test.go	Adds four targeted tests: happy path handle resolution, ErrNotFound wrapping, ErrIncompleteHandle, and ErrTerminated (verifies runtime is never called for terminated sessions).
backend/internal/httpd/controllers/sessions.go	Adds ErrTerminated → 409 SESSION_TERMINATED case to writeSessionError; placement in the switch is correct and does not affect other error mappings.
backend/internal/session_manager/manager.go	Adds ErrTerminated sentinel and a thin Send method that delegates to the messenger; error chain from runtimeMessenger is preserved via fmt.Errorf %w.

Sequence Diagram

sequenceDiagram
    participant User
    participant CLI as ao send (cli/send.go)
    participant Daemon as HTTP Daemon
    participant Ctrl as SessionsController
    participant Svc as sessionsvc.Service
    participant Mgr as sessionmanager.Manager
    participant Msng as runtimeMessenger
    participant DB as sqlite.Store
    participant RT as zellij.Runtime

    User->>CLI: ao send --session X --message ...
    CLI->>CLI: validate flags (usageError exit 2 if blank)
    CLI->>Daemon: POST /api/v1/sessions/X/send
    Daemon->>Ctrl: send(w, r)
    Ctrl->>Ctrl: decodeJSON, validate, stripUnsafeControlChars
    Ctrl->>Svc: Send(ctx, id, message)
    Svc->>Mgr: Send(ctx, id, message)
    Mgr->>Msng: messenger.Send(ctx, id, message)
    Msng->>DB: GetSession(ctx, id)
    DB-->>Msng: rec, ok
    alt not found
        Msng-->>Ctrl: "ErrNotFound -> 404"
    else terminated
        Msng-->>Ctrl: "ErrTerminated -> 409"
    else no handle
        Msng-->>Ctrl: "ErrIncompleteHandle -> 409"
    else ok
        Msng->>RT: SendMessage(ctx, handle, message)
        RT-->>Msng: nil
        Ctrl-->>CLI: 200 ok
        CLI-->>User: exit 0
    end

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_{Reviews (7): Last reviewed commit: "fix(send): reject terminated sessions" | Re-trigger Greptile}

[harshitsinghbhandari]

@greptile-apps review.