docs: add scoped protocol runtime failure contracts

[masarray]

Summary

Adds narrowly scoped engineering contracts beneath the existing mature root AGENTS.md; the root contract is not rewritten.

src/ARIEC60870.Master/AGENTS.md

• explicit master/session state authority
• root-cause-first loop + three-patch circuit breaker
• typed Result/status handling for timeout, DFC, no-data, cancellation and transport failures
• Stop/cancellation as a first-class deterministic path
• bounded polling/backpressure and diagnostics
• transactional session/config activation
• repeated Start/Stop resource-lifecycle and performance regression gates

src/ARIEC60870.Core/AGENTS.md

• parser ownership remains in Core
• TryParse/Result rather than exception-driven malformed-data flow
• strict length/index/checksum/time/numeric validation
• unknown protocol values preserve raw evidence instead of guessed semantics
• bounded resynchronization and hot-path allocation discipline
• deterministic positive/negative parsing regressions

Documentation-only change; protocol/runtime behavior is unchanged.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Limit parser ownership to the protocols Core implements

This unqualified ownership statement conflicts with the repository's existing architecture: docs/ARCHITECTURE.md:61-75 assigns IEC-10x ASDU and IEC-104 APDU parsing to Master, where Protocol/Iec10x/Iec10xAsduDecoder.cs and Iec104ApduParser.cs already provide the canonical implementations. As written, future work on those parsers is simultaneously required to remain in Master and prohibited as duplicated parser truth; qualify this contract as IEC-103/Core-hosted parsing, or migrate the IEC-10x parsers and architecture documentation together.

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