store no-capture URLs in terminal_url

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+status: in-progress
+
+Storing no-capture missing URLs in `terminal_url`
+=================================================
+
+Currently, when the bulk-mode ingest code terminates with a `no-capture`
+status, the missing URL (which is not in GWB CDX) is not stored in
+sandcrawler-db. This proposed change is to include it in the existing
+`terminal_url` database column, with the `terminal_status_code` and
+`terminal_dt` columns empty.
+
+The implementation is rather simple:
+
+- CDX lookup code path should save the *actual* final missing URL (`next_url`
+  after redirects) in the result object's `terminal_url` field
+- ensure that this field gets passed through all the way to the database on the
+  `no-capture` code path
+
+This change does change the semantics of the `terminal_url` field somewhat, and
+could break existing assumptions, so it is being documented in this proposal
+document.
+
+
+## Alternatives
+
+The current status quo is to store the missing URL as the last element in the
+"hops" field of the JSON structure. We could keep this and have a convoluted
+pipeline that would read from the Kafka feed and extract them, but this would
+be messy. Eg, re-ingesting would not update the old kafka messages, so we could
+need some accounting of consumer group offsets after which missing URLs are
+truely missing.
+
+We could add a new `missing_url` database column and field to the JSON schema,
+for this specific use case. This seems like unnecessary extra work.
+