[tianxiaochannel-oss88]

Summary

• add provider-aware proactive soft and hard summary coordination
• bound durable summary output and count active summaries in candidate projection budgets
• persist contiguous coverage watermarks, exact source refs, and late-result fences
• bind immutable context snapshots atomically when channel conversation branches are created
• reconstruct child context without copying parent items or following later parent supersession
• keep one strict context-length retry on the canonical summary path

Verification

• Combined Core: 358/358
• Summary coordinator: 4/4
• Issue [Bug]: Channel intent selector repeats generic clarification after content continuation #421, fallback, provider-aware hard summary, active-run isolation: 5/5
• Daemon build: pass
• git diff --check: pass
• Isolated S5 branch full Daemon: 894/894
• GitHub Node 22 CI is the merge gate for the stacked result.

Continuity v2

PR-E / S5, stacked on PR #428 until S4 merges.