v0.9.14: model-facing context_status tool — one honest remaining-budget meter

Source: tool-surface survey 2026-09-15. Codex ships `get_context_remaining` and `new_context_window`; Codewhale has nothing model-visible despite having more context machinery than anyone (compaction with a survival contract, large-output routing, tool-result spill).

The model currently flies blind about its own remaining budget, and the few estimates that exist are four unrelated estimators.

## Proposal

A model-facing `context_status` tool exposing one honest meter: "X of Y tokens used, compaction at threshold Z, last spill handle H". The numbers are already computed — the work is choosing which estimator is canonical and projecting it. Directly improves compaction behavior.

Start by surveying the existing context machinery, including compaction, large-output routing, tool-result spill, and the four current estimators. The issue names no files or tests, so locate the model-facing tool entry point and determine which estimator can be canonical. Done means exposing one consistent used/total meter, compaction threshold, and last spill handle.

Written by the indexing model from the issue text.