D-26: Pre-flight check — interactive TUI prompts detection (missing auth / /login)

[kirich1409]

Description

Detect when Claude Code in Dialogue mode can't function because the CLI will drop to an interactive TUI (missing API key, needs /login, OAuth flow, first-run setup) — show an explicit fallback screen instead of a broken-looking empty Dialogue.

Spec: Epic #250 §11 Risks row 2; docs/architecture/dialogue.md §2 pre-flight section.

Scope

Detection logic

Before AgentSessionFeature.startAgent fires for Dialogue:

1. Run claude doctor --output-format json (if available) or equivalent probe (a minimal one-shot invocation that exits quickly).
2. Inspect output: presence of apiKey / authenticated: true / absence of needs_setup.
3. If OK → proceed with Dialogue start.
4. If not OK → dispatch _preflightFailed(reason) → AgentSessionFeature sets Presentation to a .preflightError(PreflightErrorState) intermediary state.

Error screen

A dedicated view in AgentChatUI/Errors/PreflightErrorView.swift:

• Explicit headline: "Claude Code needs interactive setup".
• Details: what's missing (API key / login / plugins / etc.).
• Primary CTA: [Open as Terminal] — opens a sibling .agentTerminal session where the user can run claude interactively and complete setup.
• Secondary CTA: [Retry] — re-runs the preflight check.
• Link: "Learn more" → opens Claude Code docs.

Heuristics for common cases

Detected	Message	CTA
ANTHROPIC_API_KEY missing AND no keyring entry	"Claude is not authenticated. Set your API key or sign in."	Open as Terminal → run /login
MCP server fails to connect	"One or more plugins failed to start."	Continue (but show in session_init chip)
CLI version < minimum required for stream-json	"Your Claude Code version is too old. Upgrade to N.N+."	Open docs
Unknown error	Generic "Setup needed"	Open as Terminal

Integration

• Called from AgentSessionFeature.startAgent before .agentDialogue branch.
• For .agentTerminal — not called (raw terminal handles its own interactive prompts).

Acceptance Criteria

• Preflight check runs before Dialogue session start.
• Correct detection of: missing API key, /login needed, missing plugins.
• PreflightErrorView renders with correct reason + CTA.
• "Open as Terminal" CTA creates a sibling terminal tab and focuses it.
• Retry re-runs preflight.
• Detection runs in < 2 seconds (spinner shown during check).
• No false positives on a valid Claude setup.

Relationships

• Parent issue: EPIC: Dialogue — structured chat UI for agent sessions #250
• Blocked by: #D-21, #D-25 (Open as Terminal reuses the sibling-tab action)
• Blocks: #D-27 (a11y)