docs: observed memory plateau + measured egress from the k3s canary (LAB-2266, LAB-2586)

[27Bslash6]

Docs correction from the LAB-2266 seven-day canary, closing the loop on LAB-2586.

What the canary observed (VictoriaMetrics container_memory_working_set_bytes, two pods since #25 was applied 2026-08-31T23:25Z):

Pod	Lifetime	24 h	26 h	46 h	OOMKills
hvhlq	08-31T23:25Z → 09-02T21:21Z (46 h, node-level disk-pressure eviction, not memory)	298 MiB	342 MiB	372 MiB	0
bhcxn	09-02T22:03Z → running	319 MiB	333 MiB at 29 h	—	0

Plateau confirmed (mechanism held: high-water ratchet, not a leak), but at ~345–372 MiB — ~20 % above the ~260–310 MiB projection the #25 comments carried. Headroom to 512Mi is ~27 %, not ">65 %".

Changes (comments and docs only; no code, no resource values):

• deploy/k3s/skyline-ingester.yaml: manifest comment states the observed plateau and real headroom.
• ingester/README.md: on-cluster reality check carries the observed figures; drops the false "sits behind access no agent has" premise (the runtime reads the cluster's VictoriaMetrics).
• docs/architecture.md: k3s row cites the shipped 320 Mi / 512 Mi (was still 128 Mi / 256 Mi) and the egress measured on-cluster: ~312 MB/day at the veth, ~70 % TCP ACKs for the ~3.5 GB/day inbound firehose (300 s packet capture: one 66-byte ACK per inbound segment), ~84 MB/day ≈ 2.5 GB/month of application traffic — inside the LAB-1933 projection.

Tickets: LAB-2266 (canary close-out docs pass), LAB-2586 (memory sizing verdict).

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Updated deployment guidance with observed 24–46-hour memory usage, a 345–372 MiB plateau, and revised headroom for the 512 MiB limit.
  • Clarified health-diagnosis guidance using lab-cluster VictoriaMetrics and counter_keys growth.
  • Added memory measurements, growth rates, projected variance, and zero-OOMKill observations.
  • Added a separate verification-date column to the Hosting table.

Walkthrough

The documentation now records observed ingester memory usage, revised resource headroom, hosting verification dates, VictoriaMetrics diagnostics, and the counter_keys growth indicator.

Changes

Ingester documentation

Layer / File(s)	Summary
Observed memory sizing deploy/k3s/skyline-ingester.yaml, ingester/README.md	Memory notes now use observed 24–46-hour measurements, revised growth rates, approximately 27% headroom, and zero OOMKills.
Hosting and health diagnostics docs/architecture.md, ingester/README.md	The Hosting table now assigns verification dates per deployment option. Health documentation identifies lab-cluster VictoriaMetrics and unbounded counter_keys growth as the LAB-1775 signature.

Merge Risk: ⚪ Minimal · up to b458f

This documentation update records verification dates for hosting decisions and introduces no runtime behavior, resource-setting, or deployment changes. No current merge-readiness risk is identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title uses conventional commit syntax with the docs: prefix and accurately describes the documentation changes. It exceeds the preferred 50-character length but remains specific and relevant.
Description check	✅ Passed	The description directly explains the canary findings, documentation updates, measured memory and egress values, and affected tickets. It is clearly related to the changeset.

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Inline comments:
In `@docs/architecture.md`:
- Line 155: Update the hosting-rationale table so the Ingester → lab k3s cluster
row has its own verification date reflecting the 2026-08-29 through 2026-09-04
evidence, while preserving the original verification dates for older rows.

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