Investigate split-root state containment warning

[kentwelcome]

Make split-root sync decisions explicit so users can inspect invalid state safely without accidental pulls.

What changed

• Type state topology failures and sync eligibility decisions.
• Block escaped, duplicate-root, detached, and unverified state pulls.
• Preserve readable snapshots with actionable containment guidance.
• Cover real Git topologies and exact sync-call counts.

Evidence

• cargo test --no-fail-fast: 596/596 app and core tests passed; integration and documentation suites passed.
• make lint: 1/1 passed; formatting and diff checks passed.

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077

[Copilot]

Pull request overview

This PR strengthens split-root state safety by making state topology failures and sync eligibility explicit, ensuring users can inspect invalid or escaped state checkouts without triggering unintended git pull --ff-only operations. It also updates user-facing diagnostics and tests to reflect the new typed topology/sync decision model.

Changes:

• Introduces typed split-root topology problems and a typed state-sync eligibility decision, then routes sync behavior through that explicit gate.
• Blocks sync for unverified/escaped/detached/wrong-branch/missing/duplicate-root cases while preserving readable snapshots and improving diagnostics.
• Expands/updates core + UI tests to cover real Git topology edge cases and enforce exact sync-call counts.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
README.md	Documents split-root containment verification and the “never pull the same checkout twice” sync guarantee.
docs/development-policy.md	Updates architecture guidance to reflect typed eligibility and distinct-root state sync sequencing.
crates/spacetop/src/ui/tests/task_list.rs	Updates footer diagnostic string expectations and adds coverage for the “outside definition” guidance.
crates/spacetop/src/lib.rs	Refactors sync flow to reload after definition sync, compute eligibility, and gate state pulls accordingly; adds topology sync tests.
crates/spacetop/src/app/overview.rs	Replaces the prior probe-failure diagnostic with typed unverified problems and richer, stable UI messages.
crates/spacetop-core/tests/state_checkout_fixtures.rs	Adds stronger topology assertions (canonical roots, branch, readability) for external symlinked state checkouts.
crates/spacetop-core/src/state_checkout.rs	Implements typed topology probing and the explicit state_sync_eligibility decision function.
crates/spacetop-core/src/domain/mod.rs	Adds StateTopologyProblem, StateSyncEligibility, and StateSyncProblem to the core domain model.
AGENTS.md	Updates repo contract documentation to reflect typed-unverified state and distinct-root eligibility ownership in core.

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