feat(context,infra): compression pipeline stages 4-5 — token pruning + relevance + ToMe

- build() is now suspend: pipeline runs all stages in fixed order, each gated by level
- TOKEN_PRUNE (level 3): TokenPruner interface + LLMLingua-2 sidecar (sidecars/llmlingua)
  + HttpTokenPruner adapter (fails open if sidecar down); prunes freeform, preserves
  protected spans, skips tier-0 turns when TIER_SPLIT on
- TOME_MERGE (level 8): ToMeMerger collapses near-duplicate freeform turns (Jaccard)
- Stage 5 selection: RelevanceScorer + EmbeddingRelevanceScorer (cosine over Embedder);
  query-conditioned reorder so least-relevant freeform drops first under budget
- [orchestration] compression_level + token_pruner_url config, wired in Main
- suspend ripple fixed across builder callers/stubs

sidecars/llmlingua/README.md

@@ -0,0 +1,37 @@
+# LLMLingua-2 token-pruning sidecar
+
+Prunes low-perplexity tokens from freeform prose before it hits the local LLM, so more usable
+context fits a bounded window. Implements pipeline stage 3 (`TOKEN_PRUNE`, level 3+) — see
+`docs/plans/correx-compression-pipeline.md` §4.
+
+Python-only because LLMLingua-2 is a torch/BERT classifier with no JVM equivalent. correx calls
+it over localhost HTTP via `HttpTokenPruner`, which **fails open**: if this sidecar is down, the
+kernel passes context through uncompressed. Nothing breaks; you just don't get token pruning.
+
+## Run
+
+```bash
+cd sidecars/llmlingua
+python -m venv .venv && source .venv/bin/activate
+pip install -r requirements.txt
+uvicorn server:app --host 127.0.0.1 --port 8199
+```
+
+First `/prune` call downloads the model (~1-2 GB) and loads torch; `/health` responds immediately.
+
+## Wire into correx
+
+Set compression level ≥ 3 for the workflow and point the kernel at the sidecar:
+
+```toml
+[compression]
+level = 4
+token_pruner_url = "http://127.0.0.1:8199"
+```
+
+## API
+
+- `GET /health` → `{"status":"ok"}`
+- `POST /prune` `{"text": str, "protected": [str], "rate": 0.55}` → `{"compressed": str}`
+  - `rate` = fraction of tokens to **keep** (0.55 ≈ 45% compression)
+  - `protected` substrings (IDs, numbers, paths, code) are kept verbatim