drop 5 dead focused_context.go helpers, a self-contained unwired chain plus one orphan

[gerardrecinto]

Last of tonight's U1000 pile in ai/agent.

isOnlyLayer1: standalone predicate, no live caller anywhere. Checked isCrossDomain's call sites (the live sibling right next to it) for anything similar that should be wired to it instead, nothing does.

trimManualSection, extractManualSection, buildCompactStoresToolContext, trimStoresManualForCombinedContext: these four only call each other in a chain, none reachable from anything outside the cluster. Grepped for 'CombinedContext' or 'StoresManual' anywhere else in the codebase, zero hits - this whole chain was built and never wired to a real caller.

Build+vet+gofmt+test clean. This closes out the U1000 sweep across ai/agent from tonight's staticcheck pass - remaining known item is the copilottools.space.go Space CRUD tool family, already flagged in earlier PRs as needing explicit sign-off since it's feature-sized, not a quick cleanup.

[github-actions]

Gemini PR Review

This diff primarily consists of the removal of several functions (isOnlyLayer1, trimManualSection, extractManualSection, buildCompactStoresToolContext, trimStoresManualForCombinedContext).

• Code quality and readability

  • Removing unused or deprecated functions simplifies the codebase, improving overall readability and reducing maintenance overhead.
  • It's a positive change if these functions are no longer required.

• Potential bugs and correctness issues

  • The main correctness concern for a pure deletion is ensuring that the removed functions are indeed no longer used by any other part of the codebase. Assuming a build system and usage analysis have confirmed this (e.g., through compiler errors or IDE warnings), then the change is correct. If they were still used, this would lead to compilation failures.