Relocate substrate event records to content/events/ and document the fix-tag convention

[williamthorsen]

Problem

codeassembly#714 landed event capture and recall, writing event records at the store root ({storePath}/events/). So that events sit coherently alongside other vault content — assertions live under content/assertions/{domain}/ — the substrate should write and read event records under content/events/ instead. Separately, the capture-event skill should document how to record a solved-problem episode so such episodes are recallable as a group.

This ticket covers only the store-agnostic codeassembly substrate. Enabling a specific vault to accept events — declaring the event/assertion kinds in that vault's schema and validating its live KB — is a per-vault concern; for the coding store that is vaults.coding#14.

Context

Builds on codeassembly#714. The capture/recall machinery is store-agnostic, and kb-retrieve classifies a record as an event by its frontmatter (captured-at), not by path — so the record location can move with no recall code change. content/events/ parallels content/assertions/{domain}/, fitting the vault content layout established in vaults.coding#11.

Proposed solution

Event location. capture-event, its provision script, and kb-retrieve adopt {storePath}/content/events/ as the substrate-wide event-record location, replacing {storePath}/events/. Because classification is frontmatter-driven, kb-retrieve needs no code change — only a regression test that an event under content/events/ is recalled and classified as an event.

Solved-problem episodes. Document in the capture-event skill that a solved-problem episode is recorded as an observation tagged fix (problem and resolution in the body) — no new type. The tag makes such episodes findable as a group.

Acceptance criteria

Must have

• capture-event and the provision script write event records to {storePath}/content/events/.
• kb-retrieve recalls events from content/events/ with no code change (it classifies records by frontmatter, not path), verified by test.
• The capture-event skill documents recording solved-problem episodes as observation events tagged fix.
• New and modified behavior is covered by tests.

Should have

• User-facing documentation (the capture-event skill) reflects the content/events/ location.

References

• Builds on: codeassembly#714
• Coding-store schema (event + assertion kinds) and live-KB validation: vaults.coding#14 (merged by vaults.coding#15)
• Coordinates with: vaults.coding#11 (vault content relocation; content/events/ parallels content/assertions/)
• Follow-up: vaults.coding#12 (retire the duplicated validator and the flat bridge lines once kb-core publishes)