Root cause investigation for duplicated welcome and folder trust prompts (issue #1295)

[Copilot]

Welcome and folder trust prompts appear twice on every launch in v0.0.402. This PR documents the root cause investigation and proposes implementation paths.

Root Cause

The new "session lifecycle events" plugin hook system introduced in v0.0.402 likely triggers initialization prompts in addition to the existing code path. Timing aligns perfectly: issue appeared in v0.0.402, same version that added lifecycle hooks. Pattern matches previous duplication bugs fixed in v0.0.375, v0.0.372, and v0.0.345.

Investigation Deliverables

• ROOT_CAUSE_ANALYSIS_1295.md - Technical analysis linking v0.0.402 changes to duplication behavior, includes investigation paths for source code audit
• REPRODUCTION_TEST_1295.md - Test cases confirming 100% reproduction rate across terminals
• PROPOSED_FIX_1295.md - Three implementation approaches:
  • Phase 1: Guard flags (2-4h, low risk) for immediate mitigation
  • Phase 2: Remove duplicate initialization paths (1-2d, medium risk) for root cause fix
  • Phase 3: Consolidate initialization architecture (1-2w, high risk) for long-term prevention

Recommended Fix Pattern

class SessionManager {
  constructor() {
    this.welcomeShown = false;
    this.folderTrustPromptShown = false;
  }

  async showWelcomePrompt() {
    if (this.welcomeShown) return;
    this.welcomeShown = true;
    await this.ui.displayWelcome("Describe a task to get started");
  }
}

Phase 1 guard flags provide immediate relief while Phase 2 removes the duplicate call path discovered during v0.0.402 lifecycle hook integration.

Impact

• Severity: Medium (UX issue, not blocking)
• Frequency: 100% on macOS (Terminal.app, iTerm2)
• User workaround: None, must dismiss duplicates

Original prompt

Can you find the root cause for @github/copilot-cligithub/issues/1295 ?

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