Testing infrastructure: AGENTS.md rules + unit test framework + geohash tests (11/11 pass)

- Add AGENTS.md: full project context + mandatory testing rules for AI sessions
- Add tests/unit/ with host-compiled C unit test infrastructure
- Clean stubs approach: ESP-IDF type stubs in tests/unit/stubs/, no source modifications
- Fix geohash.c bit extraction bug (3-byte span) found by unit tests
- test_geohash: 11/11 passing with reference vectors (Munich, NYC, origin, boundaries)

1 files changed, 66 insertions, 0 deletions

diff --git a/tests/unit/Makefile b/tests/unit/Makefile
new file mode 100644
index 0000000..4adc720
--- /dev/null
+++ b/tests/unit/Makefile
@@ -0,0 +1,66 @@
+REPO_ROOT := ../..
+SECP256K1_SRC := $(REPO_ROOT)/nucula_src/components/secp256k1/libsecp256k1
+SECP256K1_INC := $(SECP256K1_SRC)/include
+SECP256K1_PRIV_INC := $(SECP256K1_SRC)/src
+SECP256K1_CFG := $(REPO_ROOT)/nucula_src/components/secp256k1
+CJSON_SRC := $(REPO_ROOT)/../esp/esp-idf/components/json/cJSON
+
+CC := gcc
+CFLAGS := -Wall -Wextra -Wno-unused-parameter -Wno-unused-function -Wno-sign-compare \
+          -std=gnu17 -g -O0 \
+          -DTEST_HOST \
+          -DENABLE_MODULE_SCHNORRSIG=1 -DENABLE_MODULE_EXTRAKEYS=1 \
+          -DECMULT_WINDOW_SIZE=8 -DECMULT_GEN_PREC_BITS=4 \
+          -include stubs/esp_err.h \
+          -I stubs \
+          -I $(SECP256K1_INC) \
+          -I $(SECP256K1_CFG) \
+          -I /usr/include/cjson
+
+LDFLAGS := -lmbedcrypto -lcjson
+
+SECP256K1_OBJ := secp256k1.o precomputed_ecmult.o precomputed_ecmult_gen.o
+
+TESTS := test_geohash test_identity test_nostr_event test_cashu test_session
+
+.PHONY: all test clean $(TESTS)
+
+all: test
+
+test: $(TESTS)
+        @echo ""
+        @echo "=== Running all unit tests ==="
+        @failed=0; \
+        for t in $(TESTS); do \
+                echo ""; \
+                echo "--- $$t ---"; \
+                ./$$t || failed=$$((failed + 1)); \
+        done; \
+        echo ""; \
+        if [ $$failed -eq 0 ]; then \
+                echo "=== ALL UNIT TESTS PASSED ==="; \
+        else \
+                echo "=== $$failed test(s) FAILED ==="; \
+                exit 1; \
+        fi
+
+$(SECP256K1_OBJ): %.o: $(SECP256K1_SRC)/src/%.c
+        $(CC) $(CFLAGS) -I $(SECP256K1_PRIV_INC) -c $< -o $@
+
+test_geohash: test_geohash.c $(REPO_ROOT)/main/geohash.c
+        $(CC) $(CFLAGS) $^ -o $@ $(LDFLAGS)
+
+test_identity: test_identity.c $(REPO_ROOT)/main/identity.c $(SECP256K1_OBJ)
+        $(CC) $(CFLAGS) -I $(SECP256K1_PRIV_INC) $< $(REPO_ROOT)/main/identity.c $(SECP256K1_OBJ) -o $@ $(LDFLAGS)
+
+test_nostr_event: test_nostr_event.c $(REPO_ROOT)/main/nostr_event.c $(SECP256K1_OBJ)
+        $(CC) $(CFLAGS) -I $(SECP256K1_PRIV_INC) $< $(REPO_ROOT)/main/nostr_event.c $(SECP256K1_OBJ) -o $@ $(LDFLAGS)
+
+test_cashu: test_cashu.c $(REPO_ROOT)/main/cashu.c
+        $(CC) $(CFLAGS) $< $(REPO_ROOT)/main/cashu.c -o $@ $(LDFLAGS)
+
+test_session: test_session.c $(REPO_ROOT)/main/session.c
+        $(CC) $(CFLAGS) $< $(REPO_ROOT)/main/session.c -o $@ $(LDFLAGS)
+
+clean:
+        rm -f $(TESTS) $(SECP256K1_OBJ)