fix: port upstream correctness fixes (#1164, #1214, #1215, #1243, #1314)

[quangdang46]

Summary

Sync the Rust port with upstream milla-jovovich/mempalace HEAD (68319dc). The previous sync ledger point recorded in port.txt was 94f1689, so this PR scans the 335 intervening commits and ports five high-priority correctness fixes that affect data integrity or KG query results.

Each fix carries the upstream issue number in a Rust code comment + a regression test mirroring the upstream test name, so the next sync session can grep for them.

Ported

Upstream	Area	Fix
#1243 (e9222b4)	MCP diary	tool_diary_write / tool_diary_read lowercase agent_name so reads are case-insensitive. Writing as Claude and reading as claude no longer silently returns zero rows.
#1214 (0b8c2c1)	KG	add_triple rejects inverted intervals (valid_to < valid_from) at write time — they would otherwise be invisible to every query and corrupt the store silently.
#1215 (4f36145 + 2e441d1)	EntityRegistry	save() now writes to a sibling .tmp, fsyncs, renames over the target, and (on Unix) fsyncs the parent directory for ext4-class durability across power loss.
#1164 (4d98b05)	MCP boundary	New config::sanitize_iso_temporal validates ISO-8601 dates / canonical UTC datetimes for as_of, valid_from, valid_to, ended. Malformed dates now produce a clear MCP error instead of silently returning empty result sets.
#1314 (e4e25ed)	MCP KG tools	tool_kg_add forwards valid_to and source_file (so historical facts can be backfilled in one call); tool_kg_invalidate resolves an omitted ended to today's date in the response instead of the literal sentinel "today".

Not in scope (explicitly deferred, recorded in port.txt)

• KG source_drawer_id provenance — requires ALTER TABLE triples migration; tracked for a follow-up PR.
• Gitignore-aware drawer prune (1d3eecb feat(sync), Python mempalace/sync.py) — larger feature, own PR.
• LLM-assisted init / --llm-* CLI flags — carried forward from the previous ledger.

Sync infrastructure

• Added .devin/skills/sync-upstream-mempalace/SKILL.md documenting the upstream-sync procedure (clone, diff against ledger commit, triage priorities, port checklist, gating commands) so future sessions can replay this loop deterministically.
• Updated port.txt with a new "Sync update — upstream HEAD 68319dc" entry listing what was ported and the updated remaining gaps.

Review & Testing Checklist for Human

• Verify the diary case-insensitive change is acceptable as a behavior change for existing palaces. Diaries written before this PR under mixed-case agent names (e.g. Claude) will continue to be readable, but only when read with the lowercased name; reading them with the original mixed-case form will now match too because the comparison is case-insensitive. New writes are stored lowercased.
• Spot-check the KG inverted-interval rejection. Confirm with mempalace_kg_add that valid_from=2026-12-31 valid_to=2026-01-01 is rejected, and that point-in-time facts (valid_from == valid_to) and open intervals (only one bound) still succeed.
• Confirm EntityRegistry.save durability on your filesystem. On macOS / non-ext4 platforms the parent-dir fsync is a no-op (errors are swallowed), which matches the Python implementation's behavior; on ext4 it is the durability guarantee.
• Read the new SKILL.md and the appended port.txt entry to confirm the sync procedure and ledger match how you want future sync sessions to work.

Test plan to verify end-to-end:

1. rustup update stable && cargo build --workspace
2. cargo test --workspace — expect 424 passed; 0 failed total (17 new regression tests added in this PR).
3. cargo clippy --workspace --all-targets -- -D warnings — expect clean.
4. Smoke-test the MCP boundary:
   • mempalace_kg_query with as_of="not-a-date" should return an MCP error.
   • mempalace_kg_invalidate without ended should return a real YYYY-MM-DD value in the response, not the string "today".

Notes

The five fixes touch four files; each fix is locally scoped so the diff stays small. No new dependencies. No schema changes. The new sanitize_iso_temporal lives next to existing Config::* helpers in crates/core/src/config.rs so it's discoverable by other MCP tools that need date validation in the future.