Improve agentic navigation asset-search reconciliation

[EricNGOntos]

Background

Agentic retrieval navigation had several residual issues around asset-search coordination, discovery hint integration, budget overdraft handling, and prompt/state verbosity. SEARCH_IMAGES/SEARCH_TABLES results could be repeated or poorly reconciled with collected owner sections, and legacy discovery selection code still shaped parts of the flow.

Scope

• Integrate discovery hints into legal navigation actions instead of a separate discovery-select fallback.
• Reconcile COLLECT + SEARCH tool results so invalid collects can be rejected before the next navigation decision.
• Simplify asset sub-agent prompts and hide internal owner/path/chunk IDs from candidate selection.
• Preserve production VLM URL handling while mapping short row IDs back to chunk IDs internally.
• Compact Agent State and Navigation Trace to avoid duplicated prompt content.
• Allow budget overdraft to complete current actions and report it to the main agent.
• Update contract coverage for the new discovery/action behavior.

Verification

• make lint
• make typecheck
• uv run python apps/api/scripts/ensure_test_environment.py --install
• uv run pytest apps/api/tests apps/worker/tests/contract -q

Target

Open PR to staging after this issue is created.