OKF migration leaves broken internal links after RebuildIndex

[mashenjun]

Summary

After generating a wiki through /remember plus /compile, running engram9 migrate-okf --write converts legacy frontmatter successfully, but engram9 validate --strict still fails because generated internal links are broken.

Reproduction

1. Start engram9 with a valid OpenAI-compatible model.

./engram9 -addr :9090 \
  -data ./claude-notes/catstock-stock-wiki \
  -model deepseek-v4-pro \
  -compile-interval 0

2. Import multiple source documents through /remember.

3. Wait for integrations to finish, then compile.

curl -sS -X POST http://127.0.0.1:9090/compile \
  -H "Content-Type: application/json" \
  -d "{}"

4. Migrate the generated wiki to OKF.

./engram9 migrate-okf --write ./claude-notes/catstock-stock-wiki/wiki

5. Validate strictly.

./engram9 validate --strict ./claude-notes/catstock-stock-wiki/wiki

Actual Result

Migration succeeds, but strict validation fails with broken internal links only.

OKF migration wrote: 94 file(s), 91 change(s)
OKF validation failed: 94 file(s), 0 error(s), 130 warning(s); strict mode treats warnings as failure

Examples:

warning semantic/index.md: broken internal link: semantic/companies/spacex.md
warning episodic/index.md: broken internal link: episodic/2026-06-24/samsung-400b-buyback.md
warning semantic/ai/anthropic-distillation-report.md: broken internal link: companies/anthropic.md

Expected Result

After migrate-okf --write, engram9 validate --strict <wiki> should pass, or at minimum generated structural indexes should not contain invalid relative links.

Suspected Causes

1. RebuildIndex() writes category sub-index links using paths relative to the wiki root even when writing wiki/semantic/index.md or wiki/episodic/index.md.

Current code in internal/storage/fs.go:

lines = append(lines, fmt.Sprintf("- [%s](%s) — %s", filepath.Base(p.relPath), p.relPath, p.desc))

For wiki/semantic/index.md, a link like semantic/companies/spacex.md resolves as wiki/semantic/semantic/companies/spacex.md, which is invalid.

2. Agent prompts still instruct legacy [[...]] links and do not require link targets to exist, so the LLM can emit links to missing pages such as semantic/companies/changxin-memory.md or semantic/commodities/oil.md.

Suggested Fix

1. Generate sub-index links relative to the sub-index file directory.
2. Add a regression test for RebuildIndex() that validates root index.md and category index.md links with engram9 validate --strict.
3. Consider constraining agent prompts or write tools so internal links point only to existing pages unless a matching page is created in the same operation.