feat!: remove protocol-1 SSE/bulk-GET compat surface (#224)

[mgabor3141]

Closes #224.

Summary

PR #191 introduced protocol 2 (snapshot.sessions / snapshot.world + the ?as=peer hub negotiation) and kept the protocol-1 per-event SSE surface alive for a staggered fleet upgrade. The fleet is on v2 now, so the compat surface is dead weight: every snapshot fan-out also shipped per-event frames to browser subscribers, and every hub carried a second event-decode path it never exercised against a v2 spoke.

This is a breaking change (feat!) → major bump to 2.0. It pairs with the other breaking changes slated for this release (e.g. the project-on-peer schema restructure), keeping the number of major bumps down.

Removed

Daemon SSE handler (cmd/gmuxd/main.go)

• initial session-upsert hydration dump for non-asPeer subscribers
• session-upsert / session-remove per-event emission branch
• peer-status per-event emission branch (browser-only; browsers get peer state from snapshot.world)
• isOwnedEvent helper (only the deleted branch called it) + TestIsOwnedEvent

Hub decoder (internal/peering/peer.go)

• sseEvent wire type
• session-upsert / session-remove handleEvent cases + the two TestHandleEvent_V1Compat tests

Deliberately kept (corrects the issue checklist)

The issue (written 2026-05-17) listed GET /v1/projects and the projects-update handler for removal. The code has since evolved so that both are load-bearing in v2, not protocol-1 compat — removing them would silently break peer project/session propagation. Verified and kept:

• projects-update SSE event, now gated to ?as=peer subscribers only. A peer hub has no snapshot.world, so it uses this event to trigger Peer.fetchProjects and refresh the peer_projects it surfaces upstream. Browsers no longer receive it (redundant with snapshot.world, which projects-update already fires via the pump → snapshotPumpRoute).
• GET /v1/projects, called by apiclient.GetProjects → Peer.fetchProjects on connect and on every projects-update. The browser doesn't use it.

The internal broadcast events stay on the in-process bus as the canonical "something changed" signal driving the snapshot pump; only the legacy wire emission and decoders were removed. ADR 0001's "Backwards compatibility" section is rewritten to document the removal and the two deliberate retentions.

Verification

• go test ./services/gmuxd/... passes under -race.
• Web suite passes unmodified (420 tests) — the v2 client never referenced the per-event types.
• Repo-wide grep: no remaining consumers of the per-event types in apps/, cli/, scripts/, and no references to isOwnedEvent / sseEvent.
• apps/website/.../architecture.md already had no GET /v1/projects row and already lists only v2 events on /v1/events — no change needed.

Manual smoke (suggested before merge)

With one daemon on main and one on this branch, confirm sessions from a pre-2.0 spoke no longer reach a 2.0 hub via the per-event path (proves the compat path is gone), while two 2.0 daemons peer normally.

[greptile-apps]

Greptile Summary

Removes the protocol-1 per-event SSE compat surface (session-upsert, session-remove, peer-status wire emission and the initial hydration dump) and the hub-side v1 decoder now that the fleet is fully on protocol 2. Two items that superficially resemble v1 artifacts — projects-update (now gated to ?as=peer subscribers only) and GET /v1/projects — are deliberately kept because they are load-bearing for peer project propagation in v2.

• main.go: Strips the non-asPeer session-upsert hydration loop, the session-upsert/session-remove/peer-status SSE emission cases, and isOwnedEvent; inverts the projects-update gate from "send unless peer" to "send only if peer."
• peer.go: Removes sseEvent wire type and the session-upsert/session-remove handleEvent branches; peer-status falls to the existing default silent-ignore path.
• Tests and ADR: Matching test cleanup and ADR rewrite documenting both the removal and the two deliberate retentions.

Confidence Score: 5/5

Safe to merge; removes only dead compat code with no in-tree v1 consumers remaining.

Every deletion has a clear mechanical justification: the v1 wire surface had no remaining callers after the fleet moved to protocol 2, the two retained items (projects-update peer trigger and GET /v1/projects) are demonstrably load-bearing in v2, and snapshotPumpRoute still routes projects-update to the world coalescer so browser subscribers continue receiving project changes via snapshot.world. Test coverage is updated to match and the race-tested suite passes.

No files require special attention.

Important Files Changed

Filename	Overview
services/gmuxd/cmd/gmuxd/main.go	Removes protocol-1 initial session-upsert hydration dump, per-event session-upsert/session-remove/peer-status SSE emission, and the isOwnedEvent helper; gates projects-update to ?as=peer subscribers only (correct: browsers get projects via snapshot.world through the world coalescer)
services/gmuxd/internal/peering/peer.go	Removes the sseEvent wire type and session-upsert/session-remove handleEvent cases; peer-status falls to default (silent ignore), snapshot.world case retains its defensive comment; no functional gap in v2 operation
services/gmuxd/cmd/gmuxd/main_test.go	Removes TestIsOwnedEvent — correct cleanup matching the deleted isOwnedEvent function
services/gmuxd/internal/peering/peering_test.go	Removes TestHandleEvent_V1CompatPerEvent and TestHandleEvent_V1CompatDropsForwardedFromKnownOrigin; drops now-unused context import; remaining test suite is intact
docs/adr/0001-snapshot-push-protocol.md	Updates the backwards-compatibility section to document the v1 wire surface removal and the deliberate retention of projects-update (peer trigger) and GET /v1/projects; accurate and matches the code changes

Sequence Diagram

sequenceDiagram
    participant Spoke as Spoke daemon
    participant Browser as Browser (v2)
    participant Hub as Hub daemon (?as=peer)

    Note over Spoke,Hub: Protocol 2 only (post this PR)

    Spoke->>Browser: snapshot.sessions (initial + on change)
    Spoke->>Browser: snapshot.world (initial + on change)
    Note over Spoke,Browser: projects-update no longer sent to browsers

    Spoke->>Hub: snapshot.sessions (initial + on change)
    Spoke->>Hub: projects-update (trigger to re-fetch projects)
    Hub->>Spoke: GET /v1/projects (fetchProjects on connect + on projects-update)
    Note over Spoke,Hub: session-upsert / session-remove / peer-status wire frames removed

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