Add branch coverage build for simulation

Adds build_coverage.sh script that:
- Builds the simulation with GCC branch coverage instrumentation
- Supports --report flag to run simulation and generate lcov HTML report
- Uses 60 second timeout with SIGINT for graceful shutdown

Also adds SIGINT handler to simulation to exit cleanly and flush coverage data.

.gitignore

@@ -1,3 +1,9 @@
 toasty_metadata_server
 toasty_chunk_server
-toasty_simulation
+toasty_simulation
+toasty_simulation_coverage
+*.gcno
+*.gcda
+*.gcov
+*.info
+coverage_html/

build_coverage.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+set -e
+
+# Build simulation with branch coverage instrumentation
+gcc src/sha256.c src/basic.c src/file_system.c src/byte_queue.c src/file_tree.c src/message.c src/tcp.c src/wal.c src/hash_set.c src/client.c src/metadata_server.c src/chunk_server.c src/random_client.c src/main.c quakey/src/lfs.c quakey/src/lfs_util.c quakey/src/quakey.c -o toasty_simulation_coverage -Iquakey/include -Iinclude -Wall -Wextra -ggdb -O0 -DMAIN_SIMULATION --coverage -fprofile-arcs -ftest-coverage
+
+echo "Coverage build complete: toasty_simulation_coverage"
+echo ""
+echo "To generate HTML coverage report:"
+echo "  1. Run: ./toasty_simulation_coverage"
+echo "  2. Run: ./build_coverage.sh --report"
+
+if [ "$1" = "--report" ]; then
+    # Reset previous coverage data
+    lcov --zerocounters --directory .
+
+    # Capture baseline coverage (before running)
+    lcov --capture --initial --directory . --output-file coverage_base.info --rc lcov_branch_coverage=1
+
+    # Run the simulation with a 60 second time limit
+    # Use SIGINT for graceful shutdown (allows coverage data to be flushed)
+    # Falls back to SIGKILL after 5 seconds if process doesn't exit
+    echo "Running simulation (60 second limit)..."
+    timeout --signal=INT --kill-after=5 60 ./toasty_simulation_coverage || true
+
+    # Capture coverage after running
+    lcov --capture --directory . --output-file coverage_test.info --rc lcov_branch_coverage=1
+
+    # Combine baseline and test coverage
+    lcov --add-tracefile coverage_base.info --add-tracefile coverage_test.info --output-file coverage.info --rc lcov_branch_coverage=1
+
+    # Remove external/system headers from report
+    lcov --remove coverage.info '/usr/*' --output-file coverage.info --rc lcov_branch_coverage=1
+
+    # Generate HTML report
+    genhtml coverage.info --output-directory coverage_html --branch-coverage
+
+    echo ""
+    echo "HTML coverage report generated in: coverage_html/index.html"
+fi

src/main.c

@@ -109,8 +109,20 @@ int main(int argc, char **argv)
 #endif
 
 #ifdef MAIN_SIMULATION
+#include <signal.h>
+
+static volatile int simulation_running = 1;
+
+static void sigint_handler(int sig)
+{
+    (void)sig;
+    simulation_running = 0;
+}
+
 int main(void)
 {
+    signal(SIGINT, sigint_handler);
+
     Quakey *quakey;
     int ret = quakey_init(&quakey, 1);
     if (ret < 0)
@@ -161,7 +173,7 @@ int main(void)
         quakey_spawn(quakey, config, "cs --addr 127.0.0.4");
     }
 
-    for (;;)
+    while (simulation_running)
         quakey_schedule_one(quakey);
 
     quakey_free(quakey);