fix(scope): retain observation leases and stop unsafe capture paths

[Epslion404]

Scope waveform reports could write a valid channel before discovering an invalid later channel, and released the resource lease between the final input-safety check and waveform fetch. Reports also opened fresh sessions after uncertain I/O. This change keeps the report in one owned or borrowed session, validates every requested channel through guarded queries before capture writes, and stops subsequent I/O after session or transport failures. Completed results survive close failures, which are recorded explicitly.

Observation uses a read-only effective configuration and the V2 pure-query snapshot contract; missing legacy-only snapshots remain unavailable. Disabled access and offline preflight failures stop before driver construction. Observation-owned factories use the construction I/O latch even for legacy descriptors, so factory initialization cannot write before channel checks. Final input-safety checks share the capture session and exclusive lease. Keeping the session open does not claim synchronized acquisition: cross-channel timing stays skipped. Advice with insufficient evidence returns advice_unavailable, and relationship helpers default to unproven timing.

Unreleased entry points and their execution contract are documented in Development, with links from the released CLI and MCP pages. Model-specific limits stay in descriptors/drivers.

Validation covers the real factory/guard/session/lease with fake transport, cross-process lock contention, invalid later channels with zero capture writes, failure cancellation, owned/borrowed lifecycle cleanup, partial V2 snapshots, advice evidence and synthetic phase regressions. The final implementation passed the full Windows Python 3.12 suite: 2677 passed, 5 skipped and 221 subtests passed. Ruff, generated Reference checks, scoped strict documentation audit, and strict MkDocs builds pass. Tests use PYTHONUTF8=1 and OPENBLAS_NUM_THREADS=1; all instrument exchanges are fake.

All five GitHub checks passed for 6337021: Linux Python 3.11/3.12, Windows Python 3.11/3.12, and documentation build. Target branch: Dev. Legacy-only snapshots remain explicitly unavailable; plugins that perform device I/O during factory construction must defer that I/O before using the observation path. Hardware support and acceptance still depend on plugin evidence.