What does registering a right-panel tab actually cost?

[radroid]

Question

Adding the panel means editing apps/web/src/components/RightPanelTabs.tsx, which upstream owns and
actively develops. That is a new row on docs/t3x/SEAMS.md, and the ledger tripwire says to
re-isolate before adding rows.

Measure it, do not estimate it:

• Churn on RightPanelTabs.tsx over the 60 days before the merge-base, using the @<epoch> form
  from the ledger's Regenerating section (the relative-suffix form silently returns 0).
• How many distinct places must change to register one tab? There are at least two case switches
  (around lines 413 and 482) plus the tab definition list around 175-225.
• Is there any extension point that avoids the edit, or is the switch the only way in?
• What would the row's risk figure be — fork lines changed × churn?

Then answer the actual decision: is a tab worth the row, or does the overlay precedent in
apps/web/src/coil/AutoResumeOverlay.tsx (fork-owned, near-zero seam) buy enough? Note the
counter-argument already on record: a map is something you keep open while working, which is a tab,
and dodging one ledger row is a poor reason to build the wrong thing.

[radroid]

Answered — measured during the loops design, docs/coil/loops-v2/UPSTREAM-DELTA.md (§ "RightPanelTabs.tsx moved") and FINDINGS.md.

Registering a right-panel tab costs 2 seam rows: apps/web/src/components/rightPanelStore.ts (churn 7 in the 60 days before the merge-base) and apps/web/src/components/RightPanelTabs.tsx (churn 14). Upstream's own AgentsPanel.tsx is the precedent: a full-size tab is one store-slice entry plus one tab entry, and the panel body itself is a new file upstream never sees. Upstream has since restyled RightPanelTabs.tsx (a Button render prop, +13, styling only) without changing the registration shape, so the cost held across a sync.

Contrast: the loops console cost zero rows because it mounted through the fork-owned <ThreadCoilOverlay> aggregator in _chat.$environmentId.$threadId.tsx, which is now free for every future per-thread fork surface. So the decision rule for #110 is: a per-thread surface goes through ThreadCoilOverlay at zero rows; only a surface that must live in the right panel's tab strip pays the two rows.