Parent

Part of #3000 and follows #4179.

Goal

Add an explicit advanced diagnostic path for heap snapshots and short memory timelines, so maintainers can ask users for stronger evidence when /doctor memory indicates high pressure.

Motivation

Single snapshots cannot distinguish transient compression peaks from sustained leaks. Heap snapshots and short trend sampling should be available, but they must be opt-in because they can be large and may contain sensitive strings from the process heap.

Proposed solution

• Add an opt-in heap snapshot command, for example /doctor memory --heap-snapshot.
• Use Node/V8 snapshot support such as v8.writeHeapSnapshot() where available.
• Save artifacts under a diagnostics directory, for example .qwen/diagnostics/memory/<timestamp>/ or an equivalent storage path.
• Write a lightweight JSON/text diagnostics report before the heap snapshot so the artifact bundle has context.
• Add a short memory timeline mode, for example /doctor memory --watch <seconds> or a bounded sampling helper, reporting RSS/heap/external deltas.
• Print a clear privacy warning before/with heap snapshot output.

Non-goals

• No automatic background heap dumps without explicit user action.
• No uploading artifacts anywhere.
• No parsing heap snapshots inside Qwen Code yet.
• No memory-pressure guard in this issue.

Acceptance criteria

• Heap snapshot generation is opt-in and degrades gracefully if unsupported.
• Output includes artifact paths and privacy guidance.
• Watch/timeline mode is bounded and cannot run indefinitely.
• Tests cover option parsing, unavailable V8 behavior, and path/report formatting.