docs(sessions): record the end-to-end R-IEKF EuRoC harness day

[Ravenwater]

Summary

Day wrapup for #429 — the end-to-end R-IEKF EuRoC harness.

• Session log docs/sessions/2026-06-30-riekf-euroc-harness.md — the arc, the two real-data bugs the harness surfaced (SqrtCovariance divergence → Joseph FullCovariance; non-finite-δx update guard), the measured MSCKF-vs-R-IEKF 2×2, and the load-bearing finding.
• CHANGELOG milestone entry (top of ## Milestones), linking the session log, marked main, post-v0.65.0 (feat(tools): drive R-IEKF through the real EuRoC pipeline #429 landed after the v0.65.0 release PR, currently unreleased).

The finding, in one line

R-IEKF runs stably end to end but underperforms the body-frame MSCKF (ATE 1.3 m vs 0.27 m; position ATE/σ 17–19 vs 2.1) — and position-norm ATE/σ cannot test the yaw-gauge thesis (standard MSCKF is already ~calibrated at 2.1 on position, since the leak is rotational). A gauge-anchored attitude-NEES is the #365 follow-up.

Changes

• docs/sessions/2026-06-30-riekf-euroc-harness.md — new session log
• CHANGELOG.md — new milestone entry

Docs only — no code changes.

Relates to #365

🤖 Generated with Claude Code

Summary by CodeRabbit

• Documentation
  • Added a new session note describing an end-to-end R-IEKF EuRoC harness evaluation, including stability observations, reported error metrics, and next-step notes.
  • Updated the changelog with a new milestone entry for 2026-06-30, linking to the session write-up and summarizing the latest harness results.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 9b84cec7-0ffd-460e-a3a7-052a40ed427e

📥 Commits

Reviewing files that changed from the base of the PR and between 3c6f4f5 and 34107ee.

📒 Files selected for processing (2)

• CHANGELOG.md
• docs/sessions/2026-06-30-riekf-euroc-harness.md

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Walkthrough

This PR adds a CHANGELOG milestone entry and a new session document recording an end-to-end R-IEKF EuRoC harness evaluation. It describes harness components, two real-data bugs found (covariance representation, non-finite update handling), measured ATE/σ results, and follow-up work.

Changes

R-IEKF EuRoC Harness Session Documentation

Layer / File(s)	Summary
CHANGELOG milestone entry CHANGELOG.md	Adds a 2026-06-30 milestone bullet describing the harness run, stability/metric comparisons, and linking to the session doc.
Session intro and harness build docs/sessions/2026-06-30-riekf-euroc-harness.md	Documents session motivation, harness components (adapter, runner, calibration, gate test), and two real-data bugs found with their mitigations.
Results, discoveries, and status docs/sessions/2026-06-30-riekf-euroc-harness.md	Reports ATE/σ comparison results, metric-validity discoveries, implementation guidance, PR merge status, and next steps (attitude-NEES metric).

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related PRs

• branes-ai/cortex#369: Updates the same CHANGELOG and adds a similar docs/sessions/* page documenting the same R-IEKF development arc, including the shared #365 yaw-gauge follow-up.

Poem
A rabbit hopped through EuRoC's maze,
Tracked R-IEKF's stability craze,
Joseph-form covariance saved the day,
Non-finite δx turned away,
Logged in docs for future gaze. 🐇📜

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is Conventional Commits formatted and accurately summarizes the docs-only harness-day update.
Description check	✅ Passed	The description covers Summary, Changes, and Linked issue, but it omits the template's Test Results and Checklist sections.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/session-2026-06-30-riekf-euroc-harness

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