Telnet (Port 17000) Migration Method — Analysis

This document captures the use cases, community findings, and feasibility analysis for adding a Telnet/port 17000 migration path to soundtouch-service as a peer of the existing XML and DNS-based methods. The /etc/hosts method stays deprecated and is intentionally kept off the visible UI options.

Sources — community discussion synthesised from gesellix/Bose-SoundTouch#221, gesellix/Bose-SoundTouch#236, scheilch/opencloudtouch#167, deborahgu/soundcork#228, deborahgu/soundcork#141, the post-EOS walkthrough PDF in docs/, Bose SoundTouch Telnet Probing thread, and flarn2006’s blog post on hacking SoundTouch.

1. Why a third method is needed

The two currently shipped methods both have hard preconditions that block real users:

The community has demonstrated a third path that needs no SSH at all: the device’s built-in diagnostic Telnet shell on TCP port 17000 accepts configuration commands that change exactly the same fields the XML method would.

1.1 Confirmed user reports (firmware 27.0.6.46330.5043500 unless noted)

So the method is plausible across at least ST 10/20/300 and Wave III/IV on the most common firmware that survived the EOS cut, without the USB unlock dance that newer firmware refuses.

2. The Telnet:17000 command set we rely on

For a broader catalogue of every telnet command the community has documented across firmware eras (the key, network, sys, envswitch, getpdo, scm, ws, swupdate, and shell-unlock families), see TELNET-COMMAND-REFERENCE.md. This section only lists the subset our migration actually drives.

2.1 URL configuration (the migration payload)

The sequence we send for soundtouch-service (community-validated in #221, #141):

sys configuration bmxRegistryUrl http://<service-host>:8000/bmx/registry/v1/services
sys configuration statsServerUrl http://<service-host>:8000
sys configuration margeServerUrl http://<service-host>:8000
sys configuration swUpdateUrl    http://<service-host>:8000/updates/soundtouch
envswitch boseurls set http://<service-host>:8000 http://<service-host>:8000/updates/soundtouch
getpdo CurrentSystemConfiguration

sys reboot is not part of this sequence. The migration flow only writes configuration — the reboot is user-initiated via the existing reboot button in the web UI, mirroring what XML/DNS migration already does. See §6.2 for how that button gains a ?method=ssh|telnet selector.

Three important details from the discussion:

1. sys configuration alone is not enough. stephan48 reported that without the envswitch boseurls set … line his typo in bmxRegistryUrl was silently restored on reboot — i.e. there is a parallel “envswitch” persistence layer that wins on next boot if you don’t also write to it. We must always issue both.
2. margeServerUrl path is bare for soundtouch-service. We mount the marge endpoints at the root of port 8000, matching what the existing XML migration writes (Manager.migrateViaXML in pkg/service/setup/setup.go sets MargeServerUrl: targetURL without any suffix). Some community recipes appended /marge because they were targeting deborahgu/soundcork, which routes marge under that sub-path. For our service: bare URL. For users redirecting to soundcork: append /marge to both margeServerUrl and the first argument of envswitch boseurls set.
3. Each command must be sent one at a time, waiting for the device’s OK response before sending the next one (foob61451’s explicit warning).

2.2 Account pairing fallback

envswitch accountid set <numeric-id> was reported by bveenker (#221) as an in-band equivalent to the HTTP /setMargeAccount call, useful when the /setMargeAccount endpoint is missing on the firmware (see §3).

2.3 Probing / preflight

• A bare TCP connect to <deviceIP>:17000 answers (no auth) on devices we care about.
• Useful read-only verification command: getpdo CurrentSystemConfiguration — prints the URLs after the changes have been applied so we can verify before rebooting.
• sys reboot is the trigger that re-reads both layers.

2.4 What Telnet:17000 cannot do

• It does not install a custom CA. So if a user wants HTTPS rather than HTTP redirection to our service (the DNS-method scenario, where resolv.conf redirection collides with the device’s TLS validation unless our root CA is trusted on the device), telnet alone won’t cover it. This is fine for our default flow, which uses plain http:// URLs to the service’s port 8000.
• It does not give us a way to read or write Sources.xml (third-party account credentials) — that still requires SSH, but for a migration we don’t actually need it.

3. The /setMargeAccount problem (issue #236, #228)

3.1 What it is

A factory-reset speaker has an empty <margeAccountUUID/> in :8090/info. The marge endpoints fail with 502 / unhandled until that field is populated, which is why several users (#221, #236) saw everything except AUX broken after migration:

POST http://<deviceIP>:8090/setMargeAccount
Content-Type: application/xml

<PairDeviceWithAccount>
  <accountId>1234567</accountId>
  <userAuthToken>soundcorkdoesntcare</userAuthToken>
</PairDeviceWithAccount>

The values are not validated by the local service, so any numeric accountId will work — soundcork’s runbook (#228) literally calls the token soundcorkdoesntcare to make the point.

3.2 Why it’s broken in practice

There are three independent failure modes observed:

3.3 Required handling

Per the user’s brief, the migration logic must:

1. Probe GET http://<deviceIP>:8090/supportedURLs and check whether /setMargeAccount is in the list before trying to POST it.
2. Time-bound the POST aggressively (e.g. ≤5s connect + ≤10s read) and treat anything over the budget as a failure rather than waiting indefinitely.
3. On either failure mode, fall back to the telnet equivalent envswitch accountid set <id> over the same pkg/telnet connection used for the URL flip. Reboot stays a user-initiated action (§6.2).
4. If telnet:17000 is also unreachable, surface a clear “your firmware does not support unattended pairing — please pair manually via the official Bose app before it goes EOS, or open SSH and use the XML method” error rather than leaving the device in a half-migrated state.

3.4 Where the <id> comes from

The device’s current account ID is already discoverable through endpoints we control:

• GET :8090/info returns <margeAccountUUID>…</margeAccountUUID>. If it is non-empty the device is already paired — reuse that ID, do not reassign. Our local marge accepts any ID, so the existing one is fine.
• If it is empty (factory reset), the user picks one in the UI:
  1. Pick from existing accounts. The setup UI lists IDs returned by DataStore.ListAccounts() so a user can re-attach a fresh device to an account that already has presets/recents/sources.
  2. Enter manually. Free-form text input, validated as exactly 7 numeric digits (the format every Bose-cloud-issued ID has had in the captures we’ve seen, and the format the wider community uses in their recipes).
  3. Randomize. A “Generate” button that picks a 7-digit number and re-rolls if it collides with an existing account in the local datastore.
• Telnet read-back (best-effort). envswitch accountid get is plausible by symmetry with envswitch accountid set (#221) but is not yet confirmed across firmwares. We will probe it during preflight; if it returns a value we cross-check it against :8090/info and warn on mismatch.

This means the user is never forced to invent a number — the common path is “the device already has an ID, reuse it” — and the manual/randomize controls only show up when the device is genuinely fresh.

4. Port 17000 availability

The diagnostic shell is gated by firmware build and product family. Anecdotally:

• ST 10 / ST 20 / ST 300 / Wave III / Wave IV on FW 27.0.6 → open.
• SA-5 with FW 9.x → some commands present (local_services on) but no remote_services on and no SSH on FW 9.0.43.23466 (#141).
• Modern firmware on some Portables → endpoint set has shrunk further.

Because of this, we cannot assume port 17000 is reachable. The migration flow must:

1. Probe with a TCP connect to <deviceIP>:17000, with a tight timeout (≤2s). A successful TCP handshake is necessary but not sufficient — some hardened firmware closes the port immediately.
2. Banner check. After connecting, read whatever the device sends within ~1s. The diagnostic shell prints a small banner (firmware-dependent); a blank read or an immediate close means we should treat it as “telnet not usable” and disable the option.
3. Capability check. Issue a no-op like getpdo CurrentSystemConfiguration and look for any non-empty response. If the device replies “Command not found” we abort and suggest XML or DNS instead.
4. Surface state to the UI. The migration form should grey out the Telnet option when the probe fails and show why (closed, banner missing, command rejected) instead of letting the user click into a dead end.

5. Implementation feasibility — Telnet client in Go

This is a feasibility check only; no code is written yet.

5.1 Protocol

“Telnet” on port 17000 is effectively a line-oriented plain-TCP shell. The device prints a small prompt (-> in the SA-5 captures from #141) and reads newline-terminated commands. There is no real Telnet option negotiation (no IAC/DO/WILL exchanges visible in the wild captures), so we don’t need golang.org/x/crypto/ssh-class machinery.

5.2 Standard-library only

A minimal client is just net.DialTimeout("tcp", host+":17000", 2*time.Second) + bufio.Scanner + time.Time-based deadlines on Conn. No third-party Telnet library is needed; github.com/reiver/go-telnet would be overkill and adds maintenance surface for no benefit. This matches the project’s KISS principle in docs/CLAUDE.md §3.

5.3 Cross-platform compatibility

net.Dial over TCP works identically on Windows, macOS, Linux and (with limitations on listening) WASM. WASM-side: soundtouch-service runs server-side anyway, so this only matters for soundtouch-cli, where TCP dial works in any target other than browser-WASM — an acceptable carve-out documented separately.

5.4 Concurrency / safety

Each migration is a single goroutine driving one device. The client must:

• enforce per-command response deadlines so a wedged device cannot stall the migration UI (mirrors the /setMargeAccount requirement);
• abort the rest of the sequence on the first non-OK response so we don’t half-write configuration;
• always close the socket on error.

5.5 Testing strategy

We can test without a real speaker by spinning up a net.Listen("tcp", "127.0.0.1:0") in the test, scripting it to consume our commands and emit canned OK/error responses. That gives us deterministic coverage for:

• happy path (all four URLs accepted),
• single-command failure → sequence aborts, no further commands sent,
• “command not found” on envswitch … → fallback path exercised,
• TCP closed mid-stream → migration aborts cleanly,
• read deadline triggers when the device hangs (the broken-state simulation).

The repo already follows the “real device responses preferred, mock servers otherwise” rule (see docs/CLAUDE.md §1, §8). The tests above are the mock-server half of that pattern.

5.6 Where it lives

The protocol client is a standalone package, not buried inside pkg/service/setup, so it can be reused from CLI tools, future setup wizards, and tests without dragging the migration manager in:

pkg/telnet/                        # NEW reusable package
  client.go                        #   Dial / SendCommand / Probe / Close
  client_test.go                   #   mock-server tests against a net.Listen

pkg/service/setup/
  telnet_migration.go              # NEW thin wrapper that imports pkg/telnet
                                   # and runs the URL config sequence
  marge_pairing.go                 # NEW /setMargeAccount probe + post + telnet
                                   # `envswitch accountid set` fallback
  setup.go                         # add MigrationMethodTelnet const + case

UI plumbing is pkg/service/handlers/web/index.html (option list) and pkg/service/handlers/web/js/script.js (toggleMigrationMethod()). The deprecated hosts option is already hidden from the dropdown when we ship this; we just add a telnet option next to xml/resolv.

5.7 Verdict

Feasible and small. Estimated scope: ~200 lines of client code in pkg/telnet, ~300 lines of tests, plus a MigrationMethodTelnet branch in Manager.MigrateSpeaker, plus the preflight probe described in §4 and the /setMargeAccount guarding described in §3.

6. Decisions made (was: open questions)

1. Account-ID generation. Resolved — see §3.4. The migration form reads :8090/info first; if margeAccountUUID is non-empty it is reused. Otherwise the UI offers (a) pick from DataStore.ListAccounts(), (b) manual entry validated as 7 numeric digits, (c) a “Generate” button that randomizes a 7-digit number and re-rolls on collision.
2. Reboot policy. Migration writes configuration only — it does not issue sys reboot itself. Reboot stays user-initiated via the existing reboot button in the web UI, the same way XML/DNS migration already works. That button’s endpoint (POST /setup/reboot/{deviceId}, Manager.Reboot(deviceIP)) gains an optional ?method=ssh|telnet query parameter; default stays ssh so existing behavior is preserved. The button itself uses a plain confirm() dialog before firing.
3. CA / HTTPS story. Telnet has no way to install a custom CA. Documented as an explicit limitation: telnet method = HTTP-only redirect to our service. Users who need end-to-end TLS must use the XML or DNS method. Possible future enhancement — a hybrid “install CA via SSH/XML, then drive the URL flip via Telnet” path. Feasibility unknown; not in this iteration.

See §9 for the as-shipped state. Section 7 below records the original forecast; the wizard grew larger during implementation and §9 documents what actually landed.

7. Summary of what changes when this lands

• New reusable package pkg/telnet — sibling of pkg/ssh, line-oriented TCP client with Dial, SendCommand, Probe, Close, all deadline-driven. No external dependencies, usable from CLI, service, and tests.
• New MigrationMethodTelnet = "telnet" constant in pkg/service/setup/setup.go plus a migrateViaTelnet branch in Manager.MigrateSpeaker.
• New pkg/service/setup/telnet_migration.go orchestrating the URL configuration sequence (§2.1) on top of pkg/telnet. Configuration only — no sys reboot here.
• New pkg/service/setup/marge_pairing.go with PairAccount(deviceIP, id): probes /supportedURLs, time-bounded POST /setMargeAccount, falls back to telnet envswitch accountid set <id> on missing/wedged endpoint.
• Manager.Reboot and HandleRebootDevice gain a method selector — signature changes to Reboot(deviceIP string, method RebootMethod) (string, error) with RebootMethodSSH (default, today’s behavior) and RebootMethodTelnet (sends sys reboot over a fresh pkg/telnet connection). Handler reads ?method=ssh|telnet from the query string.
• MigrationSummary gains TelnetReachable, TelnetBanner, TelnetCommandsAccepted, SetMargeAccountSupported, CurrentAccountID, KnownAccountIDs so the UI can show preflight outcomes and offer reuse.
• UI — web/index.html dropdown gets a telnet option (greyed out when preflight fails) and a new pane for picking/entering/randomizing a 7-digit account ID when :8090/info reports an empty margeAccountUUID. The existing reboot button gets a method selector (radio or dropdown) wired to the new query param, with confirm() before firing. The legacy hosts option stays out of the dropdown (deprecated).

8. Device compatibility today

What follows is the current best read on which devices our migrateViaTelnet flow handles end-to-end, derived from the same six sources catalogued in TELNET-COMMAND-REFERENCE.md plus the issue threads cited above. This is migration-outcome perspective; for per-command availability see the reference doc.

8.1 Proven to work end-to-end

All on the firmware-27.0.6 family, which is what survived through Bose’s end-of-service cut. Multi-reporter agreement on every row.

The exact sequence each reporter ran by hand is the sequence our migration sends (§2.1). So the migration’s happy path is exercised against five hardware variants in independent captures.

8.2 Proven to need the pairing fallback

Migration of the URLs themselves works on these models, but POST /setMargeAccount is missing or wedged on the firmware build, so pairing has to go through the telnet envswitch accountid set <id> path that setup.PairAccount already implements.

8.3 Likely to fail (but the failure is clean)

Our preflight + abort-on-first-rejection design (TestMigrateViaTelnet_CommandNotFoundAborts) means none of these scenarios leave a device half-configured. The user is told what failed and pointed to the XML or DNS method.

8.4 Unknown — would benefit from real-device verification

8.5 The S5 “valid roots” tension

S5 (the r/bose telnet-probing thread) lists only key, net, sys, getpdo as command roots that don’t return “Command not found” on its ST 10 / FW 27.0.6 — which would seem to rule out envswitch. But foob61451 on the same hardware/firmware ran envswitch boseurls set successfully (#221).

The most plausible reading is that S5 is a non-exhaustive probe, not a negative claim: the author writes “I’ve made some educated guesses and come up with the following valid commands” and never says they tested envswitch. We do not down-weight envswitch availability on the strength of S5 alone — but if a real-device run ever shows envswitch rejected on an ST 10, our preflight catches it, the migration aborts on the first non-OK response, and the user gets a clear error rather than partial state.

8.6 Failure-mode matrix

What migrateViaTelnet does in each failure mode (verified by pkg/telnet and pkg/service/setup unit tests):

8.7 TL;DR

• Green light — ST 10, ST 20, ST 300, Wave III, Wave IV on FW 27.0.6 (multi-reporter agreement).
• Yellow — ST Portable and BST20 Portable: migration works, pairing needs our fallback (already implemented).
• Red, but fails cleanly — SA-5 on FW 9.x, possibly newer ST Portable builds.
• Unverified but expected to work — ST 30, ST 520, Wave Music System I/II.

The most useful next verification step is touching a real ST 30 and ST 520 — those are the two “expected to work” models with zero concrete captures. Beyond that, every behaviour the doc predicts is exercised by the unit tests in pkg/telnet and pkg/service/setup.

9. What actually shipped (post-implementation addendum)

§7 forecast the surface area roughly; the wizard ended up larger. This section is the present-day map of the migration tab and the supporting backend pieces — kept appended rather than rewritten in place so the feasibility analysis above stays a faithful design record.

9.1 Three-axis state model

MigrationSummary now exposes the four mechanism-specific booleans that checkIsMigrated writes individually:

• XMLMigrated — parsed SoundTouchSdkPrivateCfg.xml’s URLs point at us.
• HostsMigrated — /etc/hosts carries Bose-domain redirects (the deprecated method, kept detectable for legacy speakers).
• ResolvMigrated — the /etc/resolv.conf priority-nameserver hook is in place (with CA trusted).
• TelnetMigrated — getpdo CurrentSystemConfiguration reports the service hostname.

IsMigrated is the OR. Plus IsPaired from the live :8090/info.margeAccountUUID value.

The frontend opens with a state card that surfaces three orthogonal axes derived from these flags:

Plus a Preconditions row: remote_services persistence, account pairing state, XML config backup presence. Action affordances (Trust CA Now, Download CA cert) live inline next to their verdicts.

9.2 Plan card with per-field URL editor

Replaces the XML method’s self/proxied/original dropdowns and the duplicate URL inputs that used to live inside the telnet method pane:

• Target service URL input with Save as default (POSTs to /setup/settings, preserving the *** secret-unchanged convention).
• Capabilities header: detected transports (SSH / Telnet:17000) and the recipes AfterTouch can offer given those transports.
• Service URLs table: four free-form URL inputs (Marge / Stats / SwUpdate / BmxRegistry) with on-keystroke validation (validatePlanURLs), a Soundcork-mode checkbox that flips /marge on margeServerUrl, and a Reset to defaults button.
• Account pairing section: ID input + Generate + datastore picker; the implicit intent (readPlanPairTarget) queues a pair step at Apply when the input differs from the current account_id.
• Suggested plan box: one-click conservative default — XML + HTTP when SSH works, Telnet + HTTP otherwise; “Already migrated” info state when IsMigrated is already true.

The per-field URLs feed both XML and Telnet migrations via the marge_url / stats_url / sw_update_url / bmx_url option family (see §9.6). Live preview rewrites #planned-config purely client-side on every keystroke — optimistic; the backend’s perspective gates the write via §9.4’s pre-flight.

9.3 Customize three-axis form

The <details> “Customize this migration” section replaces the old migration-method dropdown with three independent radio groups:

1. URL flip transport: XML / Telnet:17000 / Skip.
2. DNS interception: None / /etc/resolv.conf hook.
3. Local CA install: checkbox.

Each option carries a per-axis availability hint ((SSH unreachable), (already trusted), etc.) so users see why an option is disabled. applyCustomPlan orchestrates the chosen combination as a sequence of existing backend calls (/setup/migrate?method=… for each flip/resolv step plus /setup/trust-ca for standalone CA install, and the queued pair step from §9.2). Resolv already bundles a CA install, so a redundant standalone CA step is skipped. First failure aborts the rest.

9.4 Pre-flight panel

Both Apply paths run a visible pre-flight panel before any backend operation touches the speaker. Each check renders inline with the 🕐 / ⟳ / ✅ / ❌ / — idiom. On all-green the panel holds for ~700ms so the success state registers, then auto-proceeds. On any failure the panel surfaces Proceed Anyway / Cancel buttons; default is to abort.

Checks:

The HTTPS check uses use_explicit_ca=true so it exercises the trust path even when CA install is part of the plan (i.e. forward-looking). The reachability skip row is explicit (“neither SSH nor Telnet:17000 is reachable”) rather than silently dropped, per the user’s “feedback always visible” requirement.

9.5 Telnet round-trip probe — the SSH-less reachability check

REMOVED — see §9.8. Empirical testing showed the swUpdate daemon caches its target URL at boot and ignores live config writes, so the active flip described below could never reach the running daemon. The section is retained as a historical record of what was tried; the running code uses the passive observer in §9.8.

The reachability gap §7 left open for USB-unlock-refusing speakers is closed by Manager.RunTelnetRoundTripProbe (pkg/service/setup/telnet_probe.go). Sequence:

1. Telnet getpdo CurrentSystemConfiguration to capture the speaker’s current swUpdateUrl.
2. Generate a random 24-hex-char token; register a one-shot signal channel under it on the new probeRegistry (sibling field on handlers.Server).
3. Telnet sys configuration swUpdateUrl <targetURL>/probe/<token> — runtime layer only, deliberately not envswitch boseurls set …. The persistence layer keeps the original URL, so a reboot heals the device naturally if our restore step fails.
4. HTTP GET <deviceIP>:8090/swUpdateCheck — the cleanest :8090 endpoint that triggers exactly one outbound to the configured swUpdateUrl. Read-only on the cloud side (doesn’t initiate an update); independent of margeAccountUUID so it works on factory-reset speakers.
5. Wait on the registered channel up to telnetProbeTimeout (6s).
6. Telnet sys configuration swUpdateUrl <originalURL> — deferred restore so it runs even on the failure path.

The new /probe/{token}[/*] catch-all on the root router signals the matching channel when the speaker’s outbound lands. The response is a minimal <swUpdateIndex/> so the speaker’s swUpdateCheck doesn’t choke on a missing structure. The /* sub-path is registered because some firmware appends a path component to the configured swUpdateUrl.

9.6 Backend additions worth knowing

9.7 Future probe candidates

• :8090/pushCustomerSupportInfoToMarge — flagged as a potential “ask the device about itself” probe that could feed a richer device-info pane (firmware build dates, hardware revisions). Not implemented.
• Running the round-trip probe on SSH-capable speakers too (as additional validation alongside the curl-from-device HTTPS test), not just as the SSH-less fallback it is today. Subsumed by §9.8 — the round-trip probe is being removed; the passive observer is transport-agnostic and replaces it for migrated speakers.

9.8 The swUpdate daemon-cache finding and removal of §9.5

The §9.5 round-trip probe was retired after empirical testing on a fully-migrated speaker (FW 27.0.6) revealed that the swUpdate daemon caches its target URL at boot and ignores live config writes. The diagnostic sequence:

1. Manual telnet flip of both layers — sys configuration swUpdateUrl <probe-url> (runtime) and envswitch boseurls set <marge> <probe-url> (persistence). getpdo CurrentSystemConfiguration confirmed both writes stuck.
2. HTTP GET :8090/swUpdateCheck to trigger fan-out.
3. Service access log showed the device outbound landed on /updates/soundtouch (the previous swUpdateUrl value, current at the last daemon boot) and /streaming/software/update/account/<id> (a separate Bose URL the daemon hits, routed to this service by DNS interception). The probe URL was never dialed.

This falsifies the original NEXT.md hypothesis that the persistence layer would override the runtime layer for the daemon’s fan-out, and points instead at daemon-level URL caching. Two consequences:

• The §9.5 probe cannot work on migrated speakers without a reboot. The cached URL is set when the daemon starts; flipping config after that point has no effect on what the daemon dials.
• The §9.5 probe likely cannot work on unmigrated speakers either, for the same reason — the daemon caches whatever URL it read at startup, which on an unmigrated speaker is the Bose cloud URL. We have no service running with the probe URL registered on unmigrated speakers, so the original “it worked in testing” claim has no empirical basis; it likely failed silently because nothing was watching.

The honest replacement is a passive observer (see pkg/service/setup/peer_probe.go):

1. Register the device IP with an in-process observer (handlers.peerObserver, wired via PeerObserverMiddleware).
2. Nudge :8090/swUpdateCheck to make the daemon fan out something sooner than its ~5min timer.
3. Wait up to 30s for any inbound from that IP. On a migrated speaker, DNS interception means the daemon’s outbounds (update fan-out, marge polls, BMX registry calls) all funnel through this service regardless of which URL the daemon resolved internally — so reachability reduces to “did the device dial us at all.”

Endpoint: POST /setup/peer-probe/{deviceId}. No device-state mutation; safe to re-run. Returns {ok, result: {reached, observed_path, elapsed_ms}, error} with the same UI keying as the old probe (result.reached).

9.8.1 The pre-flight panel branch

The web UI’s pre-flight orchestrator (runApplyPreflight in script.js) branches on summary.is_migrated:

Per-axis booleans (xml_migrated, hosts_migrated, resolv_migrated, telnet_migrated) remain visible in the State card, so the user can see which parts of the migration are already in place even when the overall flag is false. The skip row does not attempt the active probe on unmigrated speakers — the canonical telnet flow is:

Apply telnet config → user-initiated reboot → re-run pre-flight on
the now-migrated speaker → passive observer confirms fan-out.

9.8.2 Removal trail

Removed (or scheduled for removal in a follow-up commit) at the time of §9.8 landing:

• pkg/service/setup/telnet_probe.go — RunTelnetRoundTripProbe, ProbeRegistrar, TelnetProbeResult, generateProbeToken.
• pkg/service/handlers/handlers_telnet_probe.go — HandleTelnetProbe, HandleProbeInbound, telnetProbeTimeout, telnetProbeResponse.
• pkg/service/handlers/probe_registry.go — probeRegistry + tests.
• Server.probes field.
• Routes /probe/{token}, /probe/{token}/*, /setup/telnet-probe/{deviceId}.
• The target_url query-param plumbing on the deprecated endpoint.
• script.js — checkTelnetRoundTrip (orchestrator call site removed in the commit that added the branch; function itself removed later).

isCommandNotFound and parseGetpdoConfig stay — they are also used by the migration writer (telnet_migration.go), preflight reader (telnet_preflight.go), pairing path (marge_pairing.go), and cross-check (preflight_crosscheck.go).