2 core foundation error handling

[lxsaah]

Adds the design document for milestone 1 of issue #2.

Milestone 2 is still open!

[Copilot]

Pull Request Overview

Adds a comprehensive design document for milestone 1 of issue #2, establishing the foundation for AimDB's error handling and feature flag architecture. The design addresses cross-platform error handling requirements from MCU to cloud environments with unified API surfaces.

• Defines unified DbError type with platform-conditional behavior using feature flags
• Establishes feature flag architecture for std/embedded platforms with runtime and protocol extensions
• Creates structured error taxonomy with performance constraints and observability integration

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/design/000-M1_error-feature-flags.md	Complete design document defining error handling architecture, feature flags, and cross-platform abstractions for M1 milestone
.github/chatmodes/architecture.chatmode.md	Removes project planning sections to focus purely on architecture and design patterns

[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

The condition all(not(feature = "std"), feature = "embedded") may be redundant since the design states that embedded and std are mutually exclusive. Consider simplifying to just #[cfg(feature = "embedded")] if the mutual exclusion is enforced elsewhere, or document why the explicit check is necessary.

Suggested change

	#[cfg(all(not(feature = "std"), feature = "embedded"))]
	#[cfg(feature = "embedded")]

[Copilot]

The invalid combinations list shows mqtt + embedded as invalid, but this conflicts with the IoT use case where MCUs commonly use MQTT. Consider clarifying whether this means 'MQTT over TCP is not available on embedded' or if there should be a separate mqtt-embedded feature for lightweight MQTT implementations.

Suggested change

	❌ mqtt + embedded # Network stack not available
	```
	❌ mqtt + embedded # MQTT over TCP not available on embedded; use `mqtt-embedded` for lightweight/MCU MQTT (if available)

Note: The combination mqtt + embedded is invalid because the standard MQTT implementation requires a TCP/IP stack, which is typically unavailable or unsuitable on MCU/embedded platforms. If a lightweight MQTT implementation (e.g., over custom transport or minimal TCP) is supported, use the mqtt-embedded feature instead.

[Copilot]

The 64-byte constraint assumes a specific cache line size, but MCUs often have different cache architectures or no cache at all. Consider specifying this as a general memory efficiency constraint rather than tying it to cache line size, or provide platform-specific size targets.

Suggested change

	- Error enum size ≤ 64 bytes (single cache line)
	- Error enum size ≤ 64 bytes (desktop/edge); ≤ 32 bytes recommended for MCUs. Target minimal size for memory efficiency.