docs: index the deferred integration seams and correct two stale markers

INTEGRATION-ONLY and KNOWN-LIMITATION are grep-able, but the grep answers the
wrong question. Thirty-four Go sites share the two markers and they carry four
different meanings: "declared, nothing implements it" reads exactly like
"implemented, only its I/O is unreachable from here", and neither reads
differently from a limitation that was accepted on purpose and is not coming
back. docs/deferred-seams.md sorts them, following the bucketed shape
internal/updater/doc.go already uses for its own package rather than starting a
second convention.

Sorting them turned up two markers that had outlived the condition they describe.

config.go called the modpack upload transport a deferred integration after both
backends had shipped -- LocalContextStore and S3ContextStore, selected in
cmd/felis by the shape of user_uploads_context, with the uploads PVC mounted and
the felis-uploads-s3 Secret rendered. What is still deferred is the far end:
Kaniko reading that context from inside the build Pod.

updater/doc.go listed the `felis update` CLI and the off-cluster Velocity jar read
under REMAINING INTEGRATION. Both exist -- cmd/felis/update.go, and
gatherer_host.go, which answers Velocity from the installed jar's manifest and
felis-api from the running binary's build stamp. The two nil seams that bullet
also names are real, but they belong to the in-cluster gatherer only, so the
bullet now says which caller has what and which is still empty.

The index also records the collision that makes a naive grep misleading:
docs/troubleshooting.md uses [INTEGRATION-ONLY] for something else, defined in its
own opening at :19 -- the symptom is produced by the kubelet, kaniko or a live
handshake, so it cannot be reproduced from the repository. Those twelve marks say
where a failure comes from, not that something is unbuilt, and are excluded.

Both code changes are comments. Every file:line the index cites was checked
against the line it points at.

docs/deferred-seams.md

@@ -0,0 +1,113 @@
+# Deferred integration seams
+
+`INTEGRATION-ONLY` and `KNOWN-LIMITATION` are grep-able markers in the Go source.
+This file is the index of what each one currently means, so that reading the
+unfinished face of the system does not require re-deriving it from 34 comment
+sites.
+
+It exists for two reasons. The markers do not all mean the same thing — four
+distinct states share them, and "declared, nothing implements it" reads exactly
+like "implemented, but its I/O cannot be exercised from this repo". And a marker
+outlives the condition it describes: two of them were stale when this index was
+first assembled, both claiming as future work something that had already shipped.
+
+The pattern here is the one `internal/updater/doc.go` already uses for its own
+package — state the verification boundary in buckets, so a green test suite is not
+mistaken for a finished integration. This file is the same idea across the whole
+tree.
+
+## The marker collides with a different vocabulary in troubleshooting.md
+
+`docs/troubleshooting.md` uses `[INTEGRATION-ONLY]` for something else, defined in
+its own opening at `:19`: the symptom is produced by the kubelet, kaniko or a live
+handshake, so it cannot be reproduced from the repository. Those twelve marks say
+where a failure comes from. They are not unfinished work and are not indexed below.
+A grep across `*.md` and `*.go` returns both sets; only the Go ones are seams.
+
+## Declared, nothing implements it
+
+- `internal/updates/seams.go:32` — `Notifier`. `internal/mail` sends OTP over SMTP,
+  but nothing adapts it to this interface and no in-game channel exists. `felis
+  update` passes nil deliberately: a human typing the command is the notification.
+- `internal/updates/seams.go:43` — `Applier`. Nothing applies an update anywhere. A
+  nil applier is not silent — `Run` records `errNoApplier` against every planned
+  apply, so a mis-scheduled apply is loud rather than lost.
+- `internal/updater/gatherer_integration.go:22` — the two current-version seams
+  `NewSysGatherer` leaves nil, for the in-cluster path: the k8s read of the
+  control-plane Deployment image, and the Velocity jar inspection. Both are answered
+  on the host path (see "Built" below), so this gap is specific to a caller that has
+  a cluster client instead of the node.
+- `internal/api/handlers_updates.go:21,28` — the maintenance window persists and the
+  API serves it, but the in-cluster CronJob that would hand a real window to a runner
+  does not exist. `felis update` runs with a zero window, under which every
+  `Scheduled` component degrades to a notify, so no path can currently claim an
+  apply is under way.
+- `internal/submit/blobstore.go:40` — the uploads PVC is mounted into felis-api but
+  not into the Kaniko build Pod, so a submitted context is durable at the derived
+  location without yet being readable by the build that consumes it.
+
+## Built; only its I/O is unverifiable from this repo
+
+Code exists and is unit-tested against fakes. What is missing is a host, a cluster
+or a real upstream account to run it against — not an implementation.
+
+- `cmd/felis/tui_edge_apply.go:246,274,295` — the `nft` edge fence, its idempotent
+  teardown, and the cloudflared invocation.
+- `internal/cfsetup/runner.go:18` and `internal/cfsetup/cfsetup.go:329` — the real
+  Cloudflare Tunnel and Access API calls; `internal/cfsetup/cfsetup_test.go:11`
+  drives the whole flow through a fake.
+- `internal/api/console.go:39`, `internal/api/logstream.go:236`,
+  `internal/api/logstream.go:306`, `internal/fileedit/k8sjobs.go:45` — each needs a
+  live cluster (RCON, `pods/log` follow, a Job).
+- `internal/api/handlers_access.go:170,490` — parsing real vanilla and LuckPerms
+  command output.
+
+## Deliberately accepted, not scheduled to close
+
+These are decisions, not backlog. Each names the condition under which it would be
+worth revisiting.
+
+- `internal/api/pgrepo.go:281` — the quota check and `ClaimServer` are two statements
+  (audit #4 TOCTOU). Closeable only against a real Postgres.
+- `internal/api/api.go:671` — `cooldownLimiter` is process-local, so across N api
+  replicas a caller could draw up to N OTP codes per window. The intra-replica burst
+  is closed; cross-replica bounding needs a shared store, out of scope for a
+  single-replica install.
+- `internal/submit/submit.go:436` and `internal/submit/submit_test.go:351` — a
+  post-CAS `Approve`
+  failure leaves a row indistinguishable from the benign case, so `Approve` returns a
+  distinct error naming the running build rather than allowing a blind re-drive that
+  would double-push. The alternative ordering is worse.
+- `cmd/felis/tui_edge_apply.go:246`, second marker on the same site — the fence
+  targets nftables. On a firewalld host a reload can flush the standalone table;
+  firewalld-native coordination is not handled. A missing `nft` binary fails loud
+  rather than leaving the port open.
+- `internal/api/handlers_account.go:169` — the reclaim "start fresh vs inherit"
+  choice is CODE-ONLY on the Java/Velocity side; the link-status endpoint reports
+  link completion only and does not surface it.
+
+## Wired since the marker was written
+
+- `internal/api/handlers_email_otp.go:54,223,227` and `internal/api/api.go:84` —
+  SMTP shipped on
+  2026-07-20 (`internal/mail`, wired at `cmd/felis/api.go:264`). The nil-`Mailer`
+  branch that logs the code server-side is a runtime fallback for an install with no
+  `[smtp]` section, not an unbuilt feature. The comments are accurate; the reading
+  "Felis cannot send mail" is not.
+- `internal/config/config.go:117` — was stale. It described the upload transport as a
+  deferred integration after both backends had shipped (`LocalContextStore`,
+  `S3ContextStore`, selected in `cmd/felis/api.go` by the shape of the configured
+  base). Corrected in the change that added this file; what remains deferred is only
+  Kaniko's read, indexed above.
+- `internal/updater/doc.go:44` — was stale. Its REMAINING INTEGRATION bullet listed
+  the `felis update` CLI and the off-cluster Velocity jar read, both of which exist
+  (`cmd/felis/update.go`, `internal/updater/gatherer_host.go`). Corrected in the same
+  change; the two nil seams it also names are real and remain above.
+
+## Recorded outside the code
+
+- `deploy/limbo/README.md:139` — no NetworkPolicy locks the minecraft-namespace
+  egress or the control-namespace ingress today, which is why the login pod reaches
+  `felis-api-internal:8081`. This is a conditional obligation rather than a seam: if
+  a future deployment adds either lock, it must also open that path. Spec v4.1 §21
+  asks for those policies; `cmd/felis/manifests.go` renders the game-port one.