feat(navigation): observe exact editor selection

[dubesinhower]

Summary

• add exact project/document/sheet-bound GetSelection observation with a before/after open-document freshness check
• decode selected board objects and the stable schematic line/label protobufs into KIID/UUID results using exact full type URLs
• add provisional get_editor_selection to the editor_navigation toolset
• add structured wrong-project, wrong-document, wrong-sheet-instance, ambiguity, stale-state, unsupported-type, and malformed-item refusals

Navigation MVP rationale

This is N2, the readback foundation for verified navigation. Selection mutation and cross-probe cannot claim success unless the client can observe the exact selected KIIIDs in the intended project, document, editor, and hierarchy instance.

Public naming and compatibility remain provisional under #395, so this PR is intentionally a draft.

Dependency

• depends on draft feat(navigation): observe editor capabilities #396 (N1), which depends on fix(ipc): bind operations to the requested board #390
• does not depend on draft fix(board): refuse stale locked file fallbacks #391

Behavior and refusals

The request must echo one exact identity returned by get_editor_state. GetOpenDocuments is matched before GetSelection and read again afterward because KiCad's SelectionResponse carries no response header. No first-document fallback exists.

The full observation fails closed for:

• wrong project, PCB document, or schematic instance path
• duplicate exact document identities
• document disappearance or retargeting during readback
• malformed selected protobufs or empty KIIIDs
• selected object types not represented by the bundled stable KiCad protobuf model
• unsupported commands and unreachable/closed endpoints

Intentionally unsupported

• heuristic protobuf wire decoding for unmodelled schematic symbols or other unknown objects
• treating references such as C10 as identity (N3)
• selection mutation (N4), activation/reveal (N5), and cross-probe (N6)

The vendored KiCad 10 schematic schema models lines and labels but not schematic symbols. Such selections return unsupported_capability; they are not guessed from bytes or saved files.

Verification

• cargo fmt --all -- --check — pass
• cargo test -p konnect-ipc --test mock_server_test — 44 passed, 1 ignored
• cargo test -p konnect-core editor_navigation --lib — 6 passed
• cargo test --workspace --all-targets — pass (933 core tests; all non-environmental targets passed)
• cargo clippy --workspace --all-targets -- -D warnings — pass
• xtask fix-doc-counts --check — 21 toolsets, 223 registered tools, 230 total; current
• git diff --check — pass

Remaining risks

• KiCad 10's schematic protobuf surface cannot serialize every selectable schematic object; callers receive typed unsupported results until the stable protocol expands
• the response lacks a document header; the before/after open-document readback detects context churn but cannot make the two transport calls atomic
• public request names and compatibility are awaiting maintainer direction in Design Priority 1 semantic editor navigation MVP #395

[neusse]

Same coordination request here: please pause further work on this draft while we start with #369 and land the existing stack from the bottom up. #397 is stacked on #396 and all of its earlier prerequisites, so every change below it currently ripples through the whole branch. Once #396 has been rebuilt on the final accepted IPC base and the #395 public API decisions are settled, #397 can be restacked once and reviewed against stable prerequisites. Holding here will avoid repeated rebases and keep the eventual review and test evidence meaningful.

[neusse]

The unique N2 portion of this cumulative draft has been reconstructed directly on the merged N1 foundation as #491.

#491 preserves the original authorship, retains the already-merged safety work and tests, and passes the complete local gate. This old stacked draft is now superseded and is being closed so there is only one active implementation path.