feat(flight-finder): implement milestone M1 - domain model and skill contract

skills/flight-finder/references/source-viability.md

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+# Flight Finder Source Viability
+
+This note records bounded live checks for the first implementation pass.
+
+It is intentionally operational, not aspirational: if a source is blocked here, the skill must treat it as blocked unless later evidence replaces this note.
+
+## Required sources
+
+- KAYAK
+- Skyscanner
+- Expedia
+- airline direct-booking cross-check
+
+## Status
+
+Checked on `2026-03-30` from Stefano's MacBook Air, with no VPN active, using the existing local `web-automation` / CloakBrowser probe scripts.
+
+Route used for bounded checks:
+
+- `DFW -> BLQ`
+- outbound date: `2026-05-30`
+- travelers: `3 adults`
+
+### KAYAK
+
+- Status: `viable`
+- Probe: `node flight_kayak_sweep.mjs DFW BLQ 3 /tmp/flight-finder-kayak-dates.json ...`
+- Evidence:
+  - title returned as `DFW to BLQ, 5/30`
+  - results included multiple one-stop itineraries with parsed USD fares such as `$877`, `$949`, `$955`
+  - direct-booking hints were visible for British Airways on at least some results
+- Implementation note:
+  - KAYAK can be a primary source in this first implementation pass
+  - parsed text is workable, but still brittle enough that bounded retries and status fallback remain necessary
+
+### Skyscanner
+
+- Status: `viable`
+- Probe: `node tmp_skyscanner_probe.mjs 'https://www.skyscanner.com/transport/flights/dfw/blq/260530/?adultsv2=3&cabinclass=economy&rtn=0'`
+- Evidence:
+  - title returned as `Cheap flights from Dallas to Bologna on Skyscanner`
+  - results page exposed concrete prices, total trip prices, stops, and itinerary text
+  - one-stop and multi-stop options were visible in the captured text
+- Implementation note:
+  - Skyscanner is viable for bounded result capture in this first pass
+  - itinerary extraction should still be treated as text-scrape, not a stable API
+
+### Expedia
+
+- Status: `viable`
+- Probe: `node tmp_expedia_probe.mjs 'https://www.expedia.com/Flights-Search?...'`
+- Evidence:
+  - title returned as `DFW to BLQ flights`
+  - results page exposed current lowest price, airline/stops filters, and concrete per-traveler options such as `$877`, `$949`, `$961`
+  - Expedia text already surfaced some itinerary summaries in a report-friendly format
+- Implementation note:
+  - Expedia is viable for bounded result capture in this first pass
+  - as with the other aggregators, source-specific timeouts and fallback rules are still required
+
+### Airline direct-booking cross-check
+
+- Status: `degraded`
+- Probe: `node tmp_skyscanner_probe.mjs 'https://www.united.com/en/us/fsr/choose-flights?...'`
+- Evidence:
+  - United's booking shell loaded and recognized the route / date context
+  - the search then returned `united.com was unable to complete your request. Please try again later.`
+- Implementation note:
+  - direct-airline cross-checking remains in scope, but it should be treated as best-effort in the first pass
+  - when a direct site fails or refuses completion, the skill should record the failure explicitly instead of hanging or pretending a clean cross-check happened
+
+## Scope decision for implementation pass 1
+
+- Primary bounded search sources: `KAYAK`, `Skyscanner`, `Expedia`
+- Direct-airline cross-check: `best-effort / degraded`
+- The skill should continue if the direct-airline step fails, but the report must say that the direct cross-check was not fully completed