[ShahriarAhnaf]

Closes #56

The model: the sim binary is the simulator and the source of truth. pippy installs it, runs it, and turns its output into Python objects and pytest results. Anything the binary does (several machines, Python scripted peers via parts:, media, bridges, --record, traces) works from Python because Python just calls the binary.

Removed (breaking, 0.5.0)

• Renode/C# backend: _RenodeBackend, the pythonnet/coreclr loader, the Simantic.Core install, the pythonnet dependency.
• backend= on Sim/run_firmware, --sim-backend, the sim_backend fixture, BACKENDS, engine_dir, ServerNotConfigured, Sim(show_logs=).
• run_firmware(server=, use_cached=): retired C# CLI flags with no pyrite equivalent.
• run_scenario(trace_symbols=, trace_memory=, trace_interrupts=, engine_dir=) and ScenarioRun.symbol_trace/memory_trace: replaced by args=.

Changed

• run_firmware runs sim <MCU> run --elf … --timeout ….
• run_scenario writes the scenario, runs sim run --scenario … --record DIR --frames F [args…] and builds ScenarioRun from uart.jsonl/isr.jsonl/log.jsonl. New: args= (any sim run flag), ScenarioRun.frames, .stdout (trace lines), .stderr (peer output); a non-zero exit raises SimError. No more NotSupported for parts:, multi-machine or network services.
• pytest test.yaml items go through run_scenario.
• No wall-clock kill around sim. It was timeout*4+30, which killed a legitimate 10 s run on a loaded host. --timeout ends runs in virtual time; the plugin still judges a manifest's wall: budget.
• Sim stays on the in-process pyrite engine: single machine, stepping/debugging. Its NotSupported messages point at run_scenario.
• README, docs/session-api.md, docs/writing-tests.md rewritten binary-first.

Checked

• SIMANTIC_SIM=<sim 0.8.5> uv run pytest -q: 175 passed, 12 skipped.
• run_scenario on an STM32H753 scenario with two Python UART peers and a CAN peer, 10 s, args=["--trace-symbol","SysTick_Handler"]: 306 UART records, 9836 SysTick hits (identical to running the binary directly), peers' output in stderr.
• sim-fixtures manifests via the plugin (run from sim-fixtures): stm32f407 can-loopback, can-counterpart, can-2node, nucleo-f401re mips-profile: 4 passed. stm32f407 uart-counterpart fails identically under plain sim run --scenario (fixture/engine, not pippy).

Known

• ScenarioRun.uart_records[*]["bytes"] is rebuilt from recorded text (latin-1), not byte-exact for non-UTF-8 output.
• test_run_scenario_with_a_scripted_peer_goes_through_the_binary runs only with SIMANTIC_PARTS_MANIFEST set (no parts: manifest on sim-fixtures main).
• docs/writing-tests.md still describes the examples-repo sample as Sim-based in places; that sample needs porting in simantic-dev/examples.

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