context-guard: document verified auto-compact-window interplay with zones

[kyle-sexton]

Context

Lane 3 of the pocock-course-lanes effort (#2901) verified the auto-compact configuration surface against primary sources (contract: docs/topics/pocock-course-lanes/PLAN.md, verdicts C1-C3 two-pool incl. the shipped binary schema autoCompactWindow:at().int().min(1e5).max(1e6)), but context-guard's docs never mention it. Consumers tuning zone bands have no guidance on how the bands relate to the auto-compact trigger, and the PostCompact marker's recorded trigger: manual|auto|unknown field is undocumented in the reader contract's consumer guidance.

Proposed work

• Add a short verified note to context-guard's README and/or reader contract covering: autoCompactWindow (settings.json, 100,000 to 1,000,000), CLAUDE_CODE_AUTO_COMPACT_WINDOW (highest precedence), autoCompactEnabled / DISABLE_AUTO_COMPACT, each with its verification as-of.
• State the interplay guidance: zone band thresholds should sit BELOW the effective auto-compact trigger so the operator reaches a boundary decision before the harness compacts for them (the house auto-compact stance adopted in lane 3: auto-compact firing means the boundary decision was left too late).
• Document the marker's trigger field for consumers (already captured by post-compact-mark.sh; currently consumers treat all triggers identically, which is deliberate; note the track-on-event condition recorded in docs/upstream/aihero-course.md lane 3).
• Record the vendored Boris anchor (playbooks/boris section 64: rot reported at 300k-400k, CLAUDE_CODE_AUTO_COMPACT_WINDOW=400000) as a named practitioner anchor, never an adopted number, consistent with claim-ladder bucket ii.

Acceptance criteria

• context-guard docs name the three auto-compact config surfaces with verification as-of dates
• The zones-below-trigger guidance is stated with its rationale
• The marker trigger field is documented for consumers, with the deliberate no-differentiation stance and its track-on-event condition
• No band value or folklore figure is adopted as a number; anchors carry named provenance

References

• docs/topics/pocock-course-lanes/PLAN.md (verdict table C1-C3; claim ladder as amended by audit A1)
• docs/upstream/aihero-course.md lane 3 rows
• plugins/context-guard/hooks/post-compact-mark.sh (trigger capture)
• session-flow: aihero course lane 3: compaction doctrine (fork-beats-compaction, auto-compact stance, evidence-degraded marker) #2901 (lane), context-guard: reader-contract advisory-injection section predates the 0.5.0 audience split (aihero lane 2) #2973 (reader-contract drift, adjacent)

Metadata

Field	Value
Category	unspecified
Area	context-guard
Ecosystem	unspecified