Tasks: Telemetry for task lifecycle events #1259

Repo: coder/coder

Scope: Add task lifecycle fields to Task telemetry to enable pause/resume analysis.

Problem: The current telemetry Task struct only has basic status. To analyze task lifecycle (pause/resume patterns, idle times, pause durations), we need lifecycle-specific metrics directly on Task telemetry.

Changes:

• Add lifecycle fields to telemetry.Task struct:
  • last_paused_at (optional timestamp) - when task was last paused
  • last_resumed_at (optional timestamp) - when task was last resumed
  • pause_reason (optional string) - "auto" or "manual"
  • idle_duration_ms (optional int64) - time from last AI "working" status to pause (only for paused tasks)
  • paused_duration_ms (optional int64) - time from pause to resume (only for recently resumed tasks, e.g. within past hour)
• Modify ConvertTask() to calculate these fields during snapshotting:
  • Query workspace_builds filtered by task's workspace_id for pause/resume transitions
  • For paused tasks: query workspace_app_statuses to find last "working" state, calculate idle_duration_ms
  • For recently resumed tasks: calculate paused_duration_ms from pause build to resume build timestamps
• All calculation happens during snapshot creation where database access is available

Why on Task not WorkspaceBuild:

• Task lifecycle metrics are about the TASK, not the underlying workspace build
• Direct task-centric data avoids complex correlation with workspace_id (multiple tasks could share a workspace)
• Analytics queries are simpler: filter Tasks by status/reason, no joins needed

Files:

• coderd/telemetry/telemetry.go (add fields to Task struct, update ConvertTask with queries)

Acceptance criteria:

• Task telemetry includes lifecycle fields (last_paused_at, last_resumed_at, pause_reason, idle_duration_ms, paused_duration_ms)
• Fields populated correctly for paused tasks (idle_duration_ms, pause_reason, last_paused_at)
• Fields populated correctly for recently resumed tasks (paused_duration_ms, last_resumed_at)
• Fields are null/absent for tasks that haven't been paused or resumed
• Telemetry tests verify calculation logic with mock workspace_builds and workspace_app_statuses data
• No regression in existing task telemetry

Dependencies:

• Tasks: Database migrations for task lifecycle #1250
• Tasks: Manual pause endpoint #1261
• Tasks: Resume endpoint #1262

References:

• PRD: Start/Pause/Resume the Task Workspace
• RFC: Tasks: Start/Pause/Resume Lifecycle: Telemetry