docs(headless): record K4 telemetry checkpoint

docs/research/2026-07-27-slice-k4-resource-telemetry-checkpoint.md

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+# Slice K4 resource telemetry checkpoint
+
+**Date:** 2026-07-27
+**Status:** Instrumentation and CPU-wakeup correction complete; fixed-binary
+connected baselines remain active
+**Production commit:** `cb512fd0`
+
+## Outcome
+
+The Linux headless process now emits one structured resource sample at
+startup, every 30 seconds, before scheduler stop, and after terminal disposal.
+Sampling is driven by the existing process scheduler's absolute deadline. It
+does not add a worker, timer, or callback per session.
+
+Each sample reports:
+
+- working set, private bytes, virtual bytes, total CPU time, interval CPU as
+  both core-equivalent and machine-normalized percentages;
+- managed live, heap, fragmentation, committed and allocated bytes, memory
+  load, GC pause percentage, and generation counts;
+- process thread/handle counts and Linux file/socket descriptors;
+- configured, in-world, faulted, reconnecting, and converged Runtime roots,
+  entity/inventory totals, and exact host-lease count;
+- scheduler waits, turns, catch-up collapses, late-deadline count, mean and
+  maximum lateness;
+- shared-content lease count, mapped virtual bytes, disposal state, and final
+  convergence.
+
+No account password or credential reference is included in this schema.
+
+## Two-account connected evidence
+
+One native Linux process connected the two locally available accounts:
+
+- `testaccount` / `+Acdream`
+- `testaccount2` / `+Horan`
+
+Both entered Rynthid and maintained independent Runtime roots and movement.
+The user asked that this process stay running for the retail-observer gate.
+
+The first process sample after both world entries reported:
+
+| Metric | Value |
+|---|---:|
+| private bytes | 207,966,208 |
+| working set | 191,553,536 |
+| managed live bytes | 71,108,368 |
+| threads | 16 |
+| handles | 115 |
+| Linux descriptors | 114 |
+| socket descriptors | 3 |
+| shared content leases | 2 |
+| mapped package virtual bytes | 29,908,271,024 |
+
+The roughly 29.9 GB mapped-package value is address space, not resident or
+private memory. The mmap remains shared and demand-paged.
+
+After movement and additional portal/density activity, the latest recorded
+sample before this checkpoint reported 305,393,664 private bytes, 332,742,656
+working-set bytes, 139,609,360 managed live bytes, 418 entities, 16 threads,
+117 handles, and the same three socket descriptors. Entity count changed from
+187 to 418 during that interval, so the memory delta is not treated as a
+same-workload per-session ceiling.
+
+## Scheduler finding and correction
+
+The connected samples exposed two distinct scheduler problems:
+
+1. scheduler deadlines began during host construction, before sequential
+   account connects completed, producing a false initial catch-up and a
+   roughly 615 ms maximum-lateness sample;
+2. the final positive sub-millisecond `Task.Delay` remainder rounded down to
+   zero on Linux, causing millions of wait-loop turns between actual 15 ms
+   simulation deadlines.
+
+The correction:
+
+- rebases every session and observation deadline exactly once after all
+  configured sessions enter the world;
+- refuses to rebase a scheduler that has already dispatched;
+- rounds only positive sub-millisecond timer waits up to one millisecond;
+- retains the 15 ms absolute simulation cadence and bounded catch-up rules.
+
+The process still under user observation was intentionally not restarted, so
+its high wait counter belongs to the pre-correction artifact. The committed
+correction is protected by deterministic rebase/lateness tests and a real
+system-timer test that fails if the scheduler busy-loops between turns.
+
+## Automated gates
+
+- Windows Headless Release: 56 passed.
+- Native Ubuntu Headless Release: 56 passed.
+- Complete Windows Release suite: 8,773 passed / 5 skipped.
+- Windows and native Ubuntu Release builds complete.
+- Diagnostics assert two configured sessions, no password text, and exact
+  two-runtime terminal convergence.
+
+## Remaining K4 gate
+
+The next connected restart must use exact binary `cb512fd0` or a documented
+descendant and prove the wait counter remains cadence-bounded, initial
+catch-up remains zero, CPU falls accordingly, and terminal resource samples
+converge. Available credentials support a two-account connected scale gate.
+The 5/10/30-session isolation and endurance dimensions therefore remain
+automated in-process gates unless additional local ACE accounts are
+provisioned.
+
+Numeric ceilings are not yet committed: they will be derived only from the
+fixed binary under matched 1- and 2-session workloads.
+
+## Rollback
+
+```text
+git revert cb512fd0
+```