fix(ai): preserve caller tool dependency chains in pruneMessages

[giulio-leone]

Summary

• trace transitive caller.toolId dependencies when computing retained tool-call IDs in pruneMessages
• prevent orphaned Anthropic programmatic tool caller references after pruning
• add regression tests for direct and transitive dependency chains plus backward-compatibility coverage

Validation

• pnpm --filter ai exec vitest --config vitest.node.config.js --run src/generate-text/prune-messages.test.ts
• pnpm --filter ai exec eslint src/generate-text/prune-messages.ts src/generate-text/prune-messages.test.ts
• pnpm --filter ai type-check
• repeated the same validation suite twice consecutively with zero failures

Closes #12504

Attribution request

If this pull request is merged, I would be grateful if contributor credit could be included in the related changelog or release notes for implementing this fix (@g97iulio1609).