fix(worker,service): UTF-8-safe content truncation

[marco-spagn]

Problem

Two call sites clamp text with a byte slice that can split a multi-byte UTF-8 rune:

• ConsolidationWorker.runConsolidation — content = content[:16000]
• SummarizeService.extractiveSummary — combined[:maxLen] + "…"

A byte cut landing mid-rune produces an invalid UTF-8 byte sequence.

The consolidation result is persisted via repo.Store, so for any non-ASCII content (accented text, CJK, emoji…) whose 16000th byte falls inside a rune, PostgreSQL rejects the INSERT with invalid byte sequence for encoding UTF8. The consolidation run is then marked failed and never succeeds for that prefix. The summarize path is less severe — json.Marshal sanitizes invalid UTF-8 to U+FFFD — but still emits a garbled trailing character.

Fix

Add a small truncateUTF8(s, maxBytes) helper (one per affected package — no shared util grab-bag exists) that backs up to a rune boundary, dropping the partial trailing rune. The result is always valid UTF-8 and within the byte budget. Both call sites use it.

func truncateUTF8(s string, maxBytes int) string {
	if maxBytes <= 0 { return "" }
	if len(s) <= maxBytes { return s }
	b := maxBytes
	for b > 0 && !utf8.RuneStart(s[b]) { b-- }
	return s[:b]
}

Tests

• Table-driven helper tests covering ASCII, 2-byte (é) and 3-byte (€) runes cut on and off boundaries, plus zero/negative budgets.
• Fuzz-style loop: cutting a multibyte string at every byte offset always yields valid UTF-8 within budget.
• extractiveSummary with a fully-CJK input truncates to valid UTF-8 with the ellipsis suffix; existing summarize tests still pass.
• go build ./..., go vet, and the full internal/worker + internal/service suites pass locally.

🤖 Generated with Claude Code

[github-actions]

✅ Test coverage: 79.19%

🔗 View workflow run

Global statement coverage; threshold = 41% (scripts/ci_coverage_check.sh).

Package	Stmts	Covered	Coverage
config	64	57	✅ 89.1%
crypto	99	87	✅ 87.9%
database	16	16	✅ 100.0%
embedding	125	118	✅ 94.4%
event	277	209	✅ 75.5%
eventschema	23	21	✅ 91.3%
graph	266	149	✅ 56.0%
grpc	821	625	✅ 76.1%
handler	983	820	✅ 83.4%
metrics	29	29	✅ 100.0%
middleware	180	154	✅ 85.6%
model	95	78	✅ 82.1%
ratelimit	38	28	✅ 73.7%
repository	953	782	✅ 82.1%
service	349	274	✅ 78.5%
telemetry	26	24	✅ 92.3%
webhook	174	145	✅ 83.3%
worker	700	516	✅ 73.7%
Global	5218	4132	✅ 79.2%

_{Generated by scripts/ci_coverage_check.sh — bump floors in the same PR that lifts coverage.}