fix: suppress nudge when all content is protected

[ranxianglei]

Summary

When all context is protected (e.g., user puts read in protectedTools and all messages contain read calls), the nudge still fires uselessly — model receives "go compress" but has nothing to compress.

PR #147's filterSuppressed only handles the case where compressible ranges exist but are filtered out. This PR adds the missing case: compressible.length === 0 && protected.length > 0 → all protected → suppress nudge.

Emergency override (98% context) still fires regardless.

Fix

lib/messages/inject/inject.ts:

const allProtected = contextRanges.compressible.length === 0 && contextRanges.protected.length > 0
const nothingToCompress = filterSuppressed || allProtected
const shouldInject = nudgeAllowed && (!nothingToCompress || emergencyOverride)

The protected.length > 0 check distinguishes "all protected" from "no refs assigned yet" (both arrays empty — edge case, not suppression).

Tests

• "nudge suppressed when all content is protected (nothing to compress)"
• "emergency override fires even when all content is protected"

752/752 tests pass.

[ranxianglei]

Superseded by #159 — #159's branch was based on this PR and the squash merge included all of #158's commits + test fixes + Scenario A coverage. Closing in favor of #159 which is now merged to master.