Run a scenario on the conversations already waiting

A new or changed scenario no longer has to wait for the next customer message: "Run on existing conversations" applies it to open conversations you pick, and shows how many match and what will be skipped before anything changes.

How it behaves

Pick the conversations: filter by status, channel, topic and when they were created, as in the inbox. Closed and spam conversations are never included. Up to 5,000 are considered, oldest first.
See the counts first: the preview says how many conversations the filters pick, how many match the scenario's conditions, how many it already ran on (they are skipped), how many sit in an inbox in shadow and how many AI field readings it will cost. Nothing changes until you press Run. A preview is valid for an hour.
Only what's safe on old conversations runs: tags, assignment, closing, internal comments, reading fields from what the customer wrote, and macros. Replies, drafts and pre-written replies never run, a helpdesk macro that would answer the customer is skipped, and Aide never asks a customer a question in an old conversation. The preview lists everything it will skip.
Once per conversation: a conversation the scenario already ran on, live or in an earlier run, is left alone, and conditions are checked again as it runs, so the final count can differ from the preview.
Your helpdesk: tags, assignment, closing and notes reach Zendesk, Gorgias and Front as they do live. An inbox in shadow keeps the changes in Aide.
Delays don't apply: a scenario set to wait before acting acts at once, since the conversations are already older than any delay.
Progress and result: the run works through the conversations a couple a second; you can close the dialog and follow it on the scenario, or stop it. The scenario then shows when it last ran on existing conversations and how many it changed, and each conversation's timeline marks the run as "Run on existing conversations".
One at a time: one run per workspace at a time, so live replies keep their pace. Owners and admins can start one.

For developers

GET and POST /v1/scenarios/{id}/backfills list a scenario's runs on existing conversations and create one: 202 with a scenario_backfill in previewing, whose preview counts fill in when it becomes ready. GET /v1/scenarios/{id}/backfills/{backfillId} reads one.
POST /v1/scenarios/{id}/backfills/{backfillId}/execution starts a ready preview (409 backfill_expired, backfill_not_ready or backfill_active); DELETE on the same path cancels it.
A conversation's scenarioRuns[].origin is backfill for a run on existing conversations, live otherwise.

All changes