## Summary
Fixes#772 — adds a short-URL form for node detail pages so operators
can paste node links into a mesh chat without bringing along a
64-hex-char public key.
## Approach
**Pubkey-prefix resolution** (no allocator, no lookup table).
- The SPA hash route `#/nodes/<key>` already accepts whatever
pubkey-shaped string the user pastes; the front end forwards it to `GET
/api/nodes/<key>`.
- When that lookup misses **and** the path is 8..63 hex chars, the
backend now calls `DB.GetNodeByPrefix` and:
- returns the matching node when exactly one node has that prefix,
- returns **409 Conflict** when multiple nodes share the prefix (with a
"use a longer prefix" hint),
- falls through to the existing 404 otherwise.
- 8 hex chars = 32 bits of entropy, which is enough for fleets in the
low thousands. Operators can extend to 10–12 chars if collisions become
common.
- The full-screen node detail card gets a new **📡 Copy short URL**
button that copies `…/#/nodes/<first 8 hex chars>`.
### Why not an opaque ID table (`/s/<id>`)?
Considered and rejected:
- Needs persistence + an allocator + cleanup story.
- IDs aren't self-describing — operators can't sanity-check them.
- IDs don't survive a DB rebuild.
- 32 bits of pubkey already buys us collision resistance with zero
moving parts.
If the directory grows past the point where 8-char prefixes routinely
collide, we can extend the minimum length without changing the URL
shape.
## Changes
- `cmd/server/db.go` — new `GetNodeByPrefix(prefix)` returning `(node,
ambiguous, error)`. Validates hex; rejects <8 chars; `LIMIT 2` to detect
collisions cheaply.
- `cmd/server/routes.go` — `handleNodeDetail` falls back to prefix
resolution; canonicalizes pubkey downstream; emits 409 on ambiguity;
honors blacklist on the resolved pubkey.
- `public/nodes.js` — adds **📡 Copy short URL** button + handler on the
full-screen node detail card.
- `cmd/server/short_url_test.go` — Go tests (red-then-green).
- `test-e2e-playwright.js` — E2E: navigates via prefix-only URL and
asserts the new button surfaces.
## TDD evidence
- Red commit: `2dea97a` — tests added with a stub `GetNodeByPrefix`
returning `(nil, false, nil)`. All four assertions failed (assertion
failures, not build errors): expected node got nil; expected
ambiguous=true got false; route 404 vs expected 200/409.
- Green commit: `9b8f146` — implementation lands; `go test ./...` passes
locally in `cmd/server`.
## Compatibility
- Existing 64-char pubkey URLs are untouched (exact lookup runs first).
- Blacklist is enforced both on the raw input and on the resolved
pubkey.
- No new config knobs.
## What I did **not** touch
- `cmd/server/db_test.go`, other route tests — unchanged.
- Packet-detail short URLs (issue scopes nodes; revisit in a follow-up
if asked).
Fixes#772
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Co-authored-by: clawbot <bot@corescope.local>
Kpa-clawbot