Switch portal tickets store to chunked lazy index

Context

#12219 is blocked because the tickets route is not actually running in lazy mode yet. @neo-opus-ada verified this on the issue, and a fresh dev check confirms it:

• apps/portal/store/Tickets.mjs still loads ../../apps/portal/resources/data/tickets.json.
• apps/portal/resources/data/tickets/index.json, manifest.json, and per-chunk files already exist from the chunked emitter work.
• apps/portal/view/news/tickets/MainContainer.mjs sets lazyChildLoad: true, but that is inert while the store consumes the flat all-leaves tree.
• buildScripts/docs/index/tickets.mjs explicitly emits both the legacy full tree and the chunked root-index shape.

This ticket preserves the missing prerequisite instead of silently widening #12219 or closing it against a flat-store premise.

The Problem

The Portal news perf track expects tickets to load only the root/group skeleton first, then fetch chunk leaves on folder expansion. Today the data exists, but the consumer still points at the legacy monolith. That means:

• first paint still pays the full tickets-tree payload cost;
• #12219 cannot honestly test lazy-aware deep-link/default-route behavior because store.get(itemId) succeeds against eagerly loaded leaves;
• the epic's chunked-index work has build artifacts but no tickets-route adoption;
• switching the store naively could expose chunk-N implementation folders as user-facing UI, which would violate the Portal news UX intent.

The Architectural Reality

• Portal.store.Tickets owns the tickets tree data source.
• buildScripts/docs/index/tickets.mjs owns the emitted legacy and chunked ticket index artifacts.
• src/app/content/TreeList.mjs owns opt-in lazyChildLoad folder expansion using childrenUrl.
• apps/portal/view/news/tickets/MainContainer.mjs already opts into lazyChildLoad, but the current store shape does not contain lazy folders.
• #12219 owns deep-link/default-route controller behavior after a partial tree exists.

The store switch is therefore the activation layer between the emitter/mechanism work and the controller work.

The Fix

Switch the tickets route from the legacy flat tickets.json consumer to the chunked tickets root index, while preserving the intended user-facing tree behavior.

The implementation must decide and verify the UI contract for chunk folders: either chunk folders are an internal lazy unit hidden from the human-facing tree, or they are rendered in a deliberate, acceptable grouping shape. The default assumption should be that raw chunk-N implementation labels are not a polished Portal UI.

Contract Ledger Matrix

Decision Record Impact

Aligned with ADR 0004 and #12204 Track B. No ADR amendment expected.

Acceptance Criteria

• Portal.store.Tickets consumes the chunked tickets root-index shape rather than the legacy all-leaves tickets.json payload.
• Initial Tickets-tab store load contains only the expected root/group/lazy-folder skeleton, not all ticket leaves.
• Expanding a lazy ticket folder fetches its childrenUrl leaves and inserts them under the correct parent without duplicate records.
• The visible Tickets tree does not regress into raw implementation noise unless that UX is explicitly accepted in the PR evidence.
• #12219 remains the controller/deep-link follow-up and can be tested against the partial tree after this lands.
• Unit or whitebox coverage proves the flat-store premise is gone and lazy expansion works for at least one backlog chunk.
• Portal visual/NL evidence confirms the Tickets tab remains usable after the store switch.

Out of Scope

• Implementing #12219 deep-link/default-route prefetch logic.
• Changing the ticket index generator shape unless a consumer contract gap is discovered during implementation.
• Changing Pull Requests or Discussions store behavior.
• Reworking ADR 0004 chunk naming or content folder layout.

Avoided Traps

• Do not code #12219 against the current flat store; that tests a dead premise.
• Do not assume lazyChildLoad: true means lazy is active; the store data must contain childrenUrl folder nodes.
• Do not expose raw chunk implementation labels as a finished human-facing UI without explicit evidence that this is acceptable.
• Do not delete the legacy tickets.json output in this ticket unless every consumer and release/data-sync path is verified.

Related

• Parent epic: #12204
• Blocks / prerequisite for: #12219
• Related mechanism: #12218
• Related emitter work: #12217

Origin Session ID: f3165fbb-7c0e-4790-8a97-b2557f5340e3

Handoff Retrieval Hints: Portal.store.Tickets tickets/index.json lazyChildLoad childrenUrl #12219 flat store blocked; buildScripts/docs/index/tickets.mjs legacy full-tree chunked root-index.