docs: README update for Layer 1 hybrid retrieval features

[cmeans-claude-dev]

Summary

• Rename "Semantic search" section → "Hybrid search" with updated content (RRF fusion, search tool, deprecated semantic_search alias, language-aware FTS, regconfig validation, graceful degradation)
• Add language support items to "Knowledge store" section (per-entry language, get_knowledge language filter, unsupported-language alerts)
• Update "Infrastructure" to mention GIN-indexed tsvector for full-text search

Closes #271. Refs #238.

QA

Prerequisites

• Read the diff

Manual tests

1. • Hybrid search section — accurately describes the search tool, RRF fusion, FTS weights, regconfig validation, graceful degradation
2. • Knowledge store section — language support items are accurate and in the right place
3. • No stale references — no remaining mentions of vector-only search as the current behavior

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[cmeans]

[QA] Round 1 — Signoff

Clean README update. Verified every claim against the merged code:

• search tool with RRF k=60 — matches semantic_search.sql ✓
• semantic_search as deprecated alias — matches #266 ✓
• Weighted tsvector fields (A=description, B=content/goal, C=tags) — matches migration ✓
• 28 stock snowball languages — matches ISO_639_1_TO_REGCONFIG ✓
• Regconfig validation with cache-refresh retry — matches #265 ✓
• Graceful degradation (either branch can be empty) — matches hybrid CTE design ✓
• Per-entry language with auto-detection via lingua-py — matches #259 tool wiring ✓
• get_knowledge language filter — matches #267 ✓
• Unsupported-language alerts — matches #269 ✓
• GIN-indexed tsvector — matches idx_entries_tsv from migration ✓
• No stale "vector-only" framing remaining ✓

CHANGELOG: ### Changed, accurate, refs #271. 848/848 pass. 3 checkboxes checked. Zero observations.

Ready for QA Signoff.

[cmeans]

[QA] Round 1 — Ready for QA Signoff. All README claims verified against merged code. Hybrid search section, knowledge store language items, infrastructure update all accurate. No stale references. 848/848 pass, 3 checkboxes checked. Applying label as final act.

[cmeans]

What about migration instructions?

[cmeans]

[QA] Round 2 — QA Failed. Migration instructions are good (new Upgrading section covers all #271 items). But 3 stale references remain: (1) tool table missing search row, semantic_search has old vector-only description; (2) env var table says 'enable semantic search'; (3) Getting started says 'Optional semantic search — for vector similarity search'. Issue #271 said to update sections referencing old search. Switching Ready for QA to QA Failed as final act.

[cmeans-claude-dev]

[Dev] QA round 2 fix: updated 3 stale references — env var table, tool table (added search row + deprecated alias row), getting started section. No remaining semantic_search references outside deprecation context and benchmark script name. Pushed 2fd9846.

[cmeans]

[QA] Round 3 — QA Failed

Round-2 findings all resolved cleanly:

• Tool table: search row added with hybrid description, semantic_search updated to "Deprecated alias" ✓
• Env var table: "enable semantic search" → "enable the vector branch of hybrid search" ✓
• Getting started: "Optional semantic search" → "Optional embedding provider", "vector similarity search" → "vector branch of hybrid search. FTS works without it" ✓

Zero remaining instances of "vector similarity search", "enable semantic search", or "Optional semantic search" (grep verified). 848/848 pass.

One new finding — tool count inconsistency:

Line 285: The server exposes 29 MCP tools.
Line 391: Full MCP API: 6 resources + 30 tools + 5 prompts

Line 285 still says 29 but the table now has 30 rows (search + semantic_search as separate tools). Line 391 was already updated to 30 in PR #266. Line 285 was not. One-line fix.

Applying QA Failed as the final act.

[cmeans]

[QA] Round 3 — QA Failed. Round-2 stale refs all fixed. One new: line 285 says '29 MCP tools' but line 391 says '30 tools' — table now has 30 rows. One-line fix.

[cmeans]

[QA] Round 4 — Signoff

Tool count fixed: both line 285 and line 391 now say 30. Zero stale references (grep verified). 848/848 pass. All #271 scope items covered (cross-checked against the issue). Zero new observations.

Ready for QA Signoff.

[cmeans]

[QA] Round 4 — Ready for QA Signoff. Tool count consistent (30/30), zero stale references, 848/848 pass. All #271 scope items covered. Applying label as final act.

[cmeans]

LGTM