docs(error-handling): add requirements and architecture documentation

[floroks]

Summary

Checklist

• I have tested my changes locally
• I have added or updated documentation
• I have linked related issues or discussions
• I have added or updated tests

Related

Notes for Reviewers

[github-actions]

📊 Coverage Report

Total line coverage: 59.32134399052694%

Full build artifacts

[github-actions]

✅ No CRAP regressions

↑ 0 regressed · ★ 0 new · ↔ 0 moved · ↓ 0 improved · 1471 unchanged · — 0 removed
✓ = clean, ▲ = moderate, ✗ = crappy; Δ = change since baseline; CC = cyclomatic complexity; Cov % = line coverage percentage

🔥 Top hot spots above threshold

	CRAP	CC	Cov %	Function	Location
✗	600.0	24	0.0	data_request	cda-sovd/src/sovd/components/ecu/mod.rs:223
✗	462.0	21	0.0	UdsManager::detect_variant	cda-comm-uds/src/variant.rs:52
✗	380.0	19	0.0	UdsManager::ecu_dtc_by_mask	cda-comm-uds/src/dtc.rs:457
✗	342.0	18	0.0	spawn_gateway_receiver_task	cda-comm-doip/src/connections.rs:580
✗	306.0	17	0.0	dop_variant_to_schema	cda-core/src/diag_kernel/schema.rs:407
✗	306.0	17	0.0	security::put	cda-sovd/src/sovd/components/ecu/modes.rs:425
✗	272.0	16	0.0	try_read	cda-comm-doip/src/connections.rs:864
✗	272.0	16	0.0	MbedtlsError::name	comm-mbedtls/mbedtls-rs/src/error.rs:67
✗	272.0	16	0.0	service::executions::ecu_reset_handler	cda-sovd/src/sovd/components/ecu/operations.rs:1339
✗	240.0	15	0.0	PhysicalType::from	cda-database/src/datatypes/data_operation.rs:394
✗	240.0	15	0.0	TlsStream::poll_read	comm-mbedtls/mbedtls-rs/src/async_stream.rs:372
✗	240.0	15	0.0	AppArgs::update_config	cda-main/src/lib.rs:251
✗	210.0	14	0.0	DoipDiagGateway::send_functional	cda-comm-doip/src/lib.rs:772
✗	210.0	14	0.0	UdsManager::send_functional_group	cda-comm-uds/src/functional_group.rs:191
✗	182.0	13	0.0	UdsManager::map_snapshots	cda-comm-uds/src/dtc.rs:353
✗	182.0	13	0.0	load_config_with_storage_override	cda-main/src/config/mod.rs:143
✗	156.0	12	0.0	update_mdd_uncompressed	cda-database/src/mdd_data/mod.rs:358
✗	156.0	12	0.0	diag_service::functional_data_request	cda-sovd/src/sovd/functions/functional_groups/data.rs:243
✗	156.0	12	0.0	post	cda-sovd/src/sovd/functions/functional_groups/locks.rs:117
✗	132.0	11	0.0	EcuManager::map_param_matching_request_from_uds	cda-core/src/diag_kernel/payload_decode.rs:463
✗	132.0	11	0.0	establish_ecu_connection	cda-comm-doip/src/ecu_connection.rs:308
✗	132.0	11	0.0	UdsManager::ecu_flash_transfer_start	cda-comm-uds/src/data_transfer.rs:187
✗	132.0	11	0.0	has_new_artifacts	cda-storage/src/recovery.rs:263
✗	132.0	11	0.0	run_with_config_ext	cda-main/src/lib.rs:417
✗	115.1	25	47.6	EcuManager::map_param_value_to_uds	cda-core/src/diag_kernel/payload_encode.rs:220

…and 106 more, see CI artifact for the full report.

[alexmohr]

suggestion: While this AGENTS.md isn't huge (yet?), the bigger an agents file is the faster it will be ignored eventually by an LLM. What worked really well for me personally is to turn the agents.md into an index and use it to link to different skills instead of trying to store everything in a single agents file.
Example: https://github.com/alexmohr/assimilate/blob/main/AGENTS.md