Retire `pano-base-feed` flag — rip FlagGate + fallback + IaC declaration (ADR 0136)

[usirin]

Stories: 1, 2, 3
TDD: no
Containment: exempt (flag retirement — no new user-facing surface; behavior already live at serves:on)

What to build

Retire the released pano-base-feed flag (base-feed/viewer-overlay split (#2322, epic #2316 leg B)), which serves on@100% in prod. Rip its FlagGate/useFlag consumers and the now-dead fallback code path so only the live path remains; delete the flag's IaC declaration in apps/web/worker/features/flagship/resources.ts and its key constant in apps/web/src/flags/keys.ts; remove the flag's own FlagGate/fallback tests. Removing this key retires the split seam itself — the base feed + PostOverlay become the unconditional source of truth.

Confirm the graduate verdict for this key before ripping (per ADR 0136 — machine nominates, human confirmed the set at Gate 1). Out of scope: any other flag in the batch (each is its own child), and any behavior change — the live path stays byte-for-byte what serves:on already delivers.

Acceptance criteria

• The pano-base-feed FlagGate/useFlag consumers and the dead fallback branch are removed; only the live path remains.
• The flag's IaC declaration in flagship/resources.ts and its key constant in flags/keys.ts are deleted; no reference to pano-base-feed remains anywhere under apps/web/ (grep-clean).
• The flag's own FlagGate/fallback tests are removed; the feature's existing behavior tests stay green (live path unchanged).
• pnpm typecheck and pnpm lint are clean.

[usirin]

claim: 34230e16-a865-4db1-8206-c6a98c273679 · 2026-07-19T23:44:40Z