Summary

• collapse the C command start APIs into one boxlite_execute entry point that takes BoxliteCommand and returns CExecutionHandle
• rename handle operations to boxlite_execution_write/wait/kill/resize_tty/free and remove exported boxlite_exec_* symbols
• reorganize C execution code into command, execution, and simple modules, with Go/tests/examples/docs updated to the single entry point
• make Ubuntu setup fail fast on incomplete apt index updates and use apt retry settings for transient mirror/DNS failures

Tests

• cargo fmt -p boxlite-c --check
• cargo build -p boxlite-c
• cargo test -p boxlite-c
• cargo clippy -p boxlite-c --tests -- -D warnings
• go test -tags boxlite_dev -run '^$' .
• go test -tags boxlite_dev -run '^(TestError_|TestExecution|TestIs|TestBoxOptions|TestRuntimeOptions|TestBuildCOptions|TestStateConstants|TestWith)' .
• cmake -S sdks/c/tests -B sdks/c/tests/build
• cmake --build sdks/c/tests/build
• cc -I sdks/c/include examples/c/01_lifecycle.c target/debug/libboxlite.dylib -Wl,-rpath,$PWD/target/debug -o /tmp/boxlite-c-lifecycle-check
• cc -I sdks/c/include examples/c/execute.c target/debug/libboxlite.dylib -Wl,-rpath,$PWD/target/debug -o /tmp/boxlite-c-execute-check
• cc -I sdks/c/include examples/c/03_streaming_output.c target/debug/libboxlite.dylib -Wl,-rpath,$PWD/target/debug -o /tmp/boxlite-c-streaming-check
• cc -I sdks/c/include examples/c/05_metrics.c target/debug/libboxlite.dylib -Wl,-rpath,$PWD/target/debug -o /tmp/boxlite-c-metrics-check
• bash -n scripts/setup/setup-common.sh scripts/common.sh scripts/setup/setup-ubuntu.sh
• git diff --check