bug(store): #574 double-quote escaping fix not applied to sanitizeFTSCandidates (match_mode="any" still errors)

[Jc-asastu]

📋 Pre-flight Checks

• I have searched existing issues and this is not a duplicate
• I understand this issue needs status:approved before a PR can be opened

📝 Bug Description

The interior-double-quote fix from #574 was applied to sanitizeFTS, but not to its sibling sanitizeFTSCandidates — the builder used by match_mode: "any". So the exact bug #574 closed is still reachable, just through the other code path.

main @ 763a6ba4:

internal/store/store.go:6585 — fixed:

func sanitizeFTS(query string) string {
	words := strings.Fields(query)
	for i, w := range words {
		w = strings.Trim(w, `"`)
		// Double interior double-quotes: FTS5 escapes a literal " inside a
		// quoted phrase by doubling it (""). ... See #574.
		w = strings.ReplaceAll(w, `"`, `""`)
		words[i] = `"` + w + `"`
	}
	return strings.Join(words, " ")
}

internal/store/relations.go:1039 — not fixed:

func sanitizeFTSCandidates(title string) string {
	words := strings.Fields(title)
	// ...
	for _, w := range words {
		w = strings.Trim(w, `"`)          // <-- only trims the ENDS
		if w != "" {
			quoted = append(quoted, `"`+w+`"`)
		}
	}
	return strings.Join(quoted, " OR ")
}

strings.Trim only removes leading/trailing quotes, so an interior quote survives and produces an unterminated FTS5 string literal.

internal/store/store.go:3167 — where match_mode: "any" selects it:

if opts.MatchMode == "any" {
	ftsQuery = sanitizeFTSCandidates(query)
} else {
	ftsQuery = sanitizeFTS(query)
}

Given the query hello"world:

builder	produced FTS5 query	result
sanitizeFTS (match_mode: "all")	"hello""world"	✅ valid
sanitizeFTSCandidates (match_mode: "any")	"hello"world"	❌ unterminated string

sanitizeFTSCandidates is also called from the relation-scan path in relations.go, where observation titles become the query — so any saved title containing a " can trip the same error there.

🔄 Steps to Reproduce

Self-contained proof of the mechanism, no Go needed (any SQLite ≥ 3.9 with FTS5):

CREATE VIRTUAL TABLE t USING fts5(x);
INSERT INTO t VALUES ('hello world');

-- what sanitizeFTSCandidates produces for  hello"world
SELECT * FROM t WHERE t MATCH '"hello"world"';   -- Error: unterminated string

-- what sanitizeFTS produces for the same input
SELECT * FROM t WHERE t MATCH '"hello""world"';  -- OK, 1 row

Through the MCP tool on main:

mem_search(query: "hello\"world", match_mode: "any")

1. Save any observation.
2. Call mem_search with a query containing an interior double-quote and match_mode: "any".
3. Search fails instead of returning results.

✅ Expected Behavior

match_mode: "any" handles interior double-quotes exactly like match_mode: "all" does after #574 — the quote is escaped by doubling, and the search returns results instead of erroring.

❌ Actual Behavior

Search error: search: SQL logic error: unterminated string (1). Try simpler keywords.

(Captured on 1.11.0, which predates #574 and therefore fails on both modes. On main the "all" path is fixed and only the "any" path still fails — that asymmetry is what this issue is about, and it is established from the source above plus the SQLite repro, not from running 1.11.0.)

🖥️ Environment

• OS: Windows
• Engram Version: 1.11.0 locally; bug analysis is against main @ 763a6ba4
• Agent / Client: Claude Code

💡 Additional Context

The fix looks like one line — reusing the same escaping sanitizeFTS already does:

w = strings.Trim(w, `"`)
w = strings.ReplaceAll(w, `"`, `""`)   // same as sanitizeFTS, see #574

Two things worth considering alongside it, entirely your call:

1. Factor the escaping into one helper used by both builders, so the two paths can't drift apart again. That drift is what produced this issue.
2. A regression test on the shared helper covering foo"bar, "foo, foo", and " alone would pin it.

Happy to open the PR with the fix plus tests once this is approved — just let me know if you'd prefer the one-line version or the shared-helper refactor.