fix: make lifecycle event mapping lossless for unknown events

[snickler]

$## Describe the Bug\n\nThe lifecycle event mapping currently appears to collapse unknown event types into SessionCreated, which can misrepresent the real lifecycle state.\n\n## Expected Behavior\n\nUnknown lifecycle events should either be preserved explicitly or mapped to a neutral/unknown state rather than a creation event.\n\n## Environment\n\n- OS: Any\n- .NET Version: .NET 10\n- Squad.SDK.NET Version: current repo state\n\n## Additional Context\n\nThis is a public event-stream semantics issue and should be validated against the intended SDK contract.\n

[github-actions]

🏗️ Squad Triage — Holden (Lead .NET Architect)

Issue: #103 — fix: make lifecycle event mapping lossless for unknown events
Assigned to: Ashford (Director of Platform & DevOps)
Reason: Issue relates to DevOps/infrastructure work

@copilot evaluation: 🔴 Not suitable — issue involves work outside the coding agent's capability profile.

Team roster:

• Holden (Lead .NET Architect) → label: squad:holden
• Fred (Director of Engineering) → label: squad:fred
• Ashford (Director of Platform & DevOps) → label: squad:ashford
• Dawes (Director of Developer Relations) → label: squad:dawes
• Drummer (Tester & QA) → label: squad:drummer
• Ralph (Work Monitor) → label: squad:ralph
• @copilot (Coding Agent) → label: squad:copilot

To reassign, remove the current squad:* label and add the correct one.

[github-actions]

🔄 Ralph — Auto-Triage

Assigned to: Drummer
Reason: Matched testing/QA role keywords
Source: role-keyword

Ralph auto-triaged this issue using routing rules.
To reassign, swap the squad:* label.

[github-actions]

🔄 Ralph — Auto-Triage

Assigned to: Drummer
Reason: Matched testing/QA role keywords
Source: role-keyword

Ralph auto-triaged this issue using routing rules.
To reassign, swap the squad:* label.

[github-actions]

🔄 Ralph — Auto-Triage

Assigned to: Drummer
Reason: Matched testing/QA role keywords
Source: role-keyword

Ralph auto-triaged this issue using routing rules.
To reassign, swap the squad:* label.

[snickler]

Spawned a focused implementation review for this issue. Current sequencing is being checked against #102; if it can run safely in parallel, I will move it into its own worktree and start the fix there. Otherwise it will wait until #102 lands.

[snickler]

Reviewed the lifecycle mapping behavior in SquadClient.

Current state:

• The worktree still maps unknown lifecycle events to SessionCreated.
• The safer contract is to preserve the event only if the SDK explicitly models it; otherwise this should be a follow-up decision before changing the mapping.

I have not changed the issue status yet because the contract decision is still needed.