#4376 stagecraft tracker: relate tickets across trackers (another repo's tracker)

Problem

The built-in @swamp/stagecraft/tracker relates tickets only within one tracker. relate looks up to in the same tracker's store and refuses anything else:

$ swamp behavior run ops-tracker relate --input issue=ops-18 --input type=related_to --input to=devswamp-25
Error: builtin not_found: no ticket 'devswamp-25'

We run two factories in two swamp repos. oikos (machines and network, tracker ops-tracker, prefix ops) and devswamp (building apps, tracker devswamp, prefix devswamp) depend on each other's work. For example, oikos's per-machine identities (ops-18) and devswamp's agent identity (devswamp-25) have to land together. The link can only be written as text in a comment, so nothing checks it, and nothing shows it in either ticket's relations or in claim/round decisions.

Proposal

Let relate (and unrelate) name a ticket in another tracker:

• A qualified reference in to, such as devswamp:devswamp-25, or a tracker/repo field alongside it, stored as an external relation.
• The relation is recorded even when the other tracker can't be read from here, as an external reference that isn't verified.
• When the other tracker is reachable (same repo, a configured path, or a serve), resolve its status at read time. A blocked_by an external ticket that isn't shipped/closed would then keep the ticket blocked, as a local one does.
• fetch_issue shows external relations with whatever status could be resolved, or "unresolved".

Alternatives

• Text references in comments (what we do today): free, but nothing checks them.
• One shared tracker for both repos, e.g. the Trello-backed @zts/trello-tracker. This changes where both factories keep their tickets just to get links.
• Beads does this already with external:<project>:<capability> dependencies and bare cross-project IDs (gastownhall/beads, docs/core-concepts/dependencies.md), and could serve as a model.

Environment

swamp 20261103.000636.0-sha.db3f6373; @swamp/stagecraft/tracker typeVersion 2026.10.12.2; Ubuntu 26.04 (WSL2).

Upstream repository: https://github.com/swamp-club/swamp-extensions

Environment

• Extension: @swamp/stagecraft@2026.10.15.2
• swamp: 20261103.000636.0-sha.db3f6373
• OS: linux (x86_64)
• Deno: 2.9.8
• Shell: /bin/bash