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ctxstream/README.md

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+# ctxstream
+
+Stream an oversized context past a small model, then construct the answer in code.
+
+Zero third-party dependencies. C++17.
+
+## Why
+
+Measured on a 4B model over a 261,226-token corpus on a 6GB card: the model swept
+every segment correctly, was asked which label was least common, and answered
+
+    Status: beta, Status: delta, Status: gamma, Status: alpha
+
+It listed the candidates instead of selecting one. An earlier run with 65 segments
+combined the partial counts wrongly. Same mistake both times, and it was the
+harness's, not the model's: a language model was asked to plan a traversal *and*
+to do aggregation arithmetic.
+
+ctxstream takes both jobs away from it.
+
+| video streaming | ctxstream |
+|---|---|
+| manifest / playlist | segment plan, computed in code, before any model call |
+| buffer | N segments in flight, latency hidden behind compute |
+| decoder | model sees ONE segment, emits `key<TAB>number`, never prose |
+| playback | reduce phase — a strategy you choose, in code |
+
+The model's only job is extraction from a window it comfortably fits.
+
+## Codebase mode
+
+A directory input is not treated as a character stream. Cutting code every N chars
+splits functions and separates a call from its definition. Instead:
+
+1. **scan** — walk the repo, skip excluded dirs and binaries, record what was
+   skipped and why
+2. **graph** — symbols (function/class/struct) per file, plus file→file edges from
+   `#include` / `import` / `require`
+3. **order** — dependency-first, so a file follows what it includes
+4. **segment** — on file boundaries, never mid-symbol; oversized files fall back to
+   line-boundary splitting
+
+```bash
+ctxstream --input ./my-repo --graph-only          # inspect the graph
+ctxstream --input ./my-repo --extract "..."       # graph, then stream
+```
+
+## Build
+
+```bash
+cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
+cmake --build build -j
+./build/test_ctxstream          # 61 checks, no model or network needed
+```
+
+## Use
+
+```bash
+ctxstream --input corpus.txt \
+  --extract "Count how many lines carry each category value in this fragment." \
+  --answer least --label Category \
+  --model gemma4:e4b --num-ctx 32768 --segment-chars 60000
+```
+
+`--answer` is `least | most | total | list`. `--plan-only` prints the segment plan
+and exits without calling a model.
+
+## Guarantees it actually enforces
+
+- **Full coverage.** Every byte lands in some segment; tests assert it. A planner
+  that drops the tail yields a confident answer over partial data.
+- **No mid-record cuts.** Segments snap back to a record boundary.
+- **Truncation is fatal, not silent.** A server that clips the prompt and answers
+  from the remainder is caught by comparing reported prompt tokens against what
+  was sent. Measured case: 50,000 tokens sent, 16,387 processed, no error raised.
+- **A partial sweep refuses a headline answer.** If any segment failed, every key
+  is undercounted, so `--answer least/most/total` exits non-zero rather than
+  printing a number.
+- **Keys with spaces survive.** `Spatial Relationship` must not become `Spatial`.
+
+## Layout
+
+```
+src/ctxstream.hpp   types + API
+src/manifest.cpp    segment planning (text)
+src/codegraph.cpp   repo scan, symbols, edges, graph-aware segmentation
+src/backend.cpp     HTTP/1.1 + minimal JSON, no libcurl
+src/pipeline.cpp    concurrent streaming, retries, progress
+src/reduce.cpp      record parsing, tally, answer construction
+src/main.cpp        CLI
+```