Add source and evidence fields to Remember decisions and errors

[bponghneng]

Goal

Improve trust and traceability for high-value memory entries by adding provenance fields.

Proposed Scope

• Add optional Source / Evidence fields to decision and error memory templates.
• Document what counts as useful evidence: PRs, issues, logs, commands, files, or conversation context.
• Update recommendation guidance to include evidence when available without inventing sources.

Value

Helps coding agents distinguish durable facts from ungrounded recollections and makes memory review easier.

Acceptance Criteria

• decision and error templates include provenance guidance.
• Recommend workflows prefer evidence when available.
• Existing entries remain valid; migration is optional.