TCP keepalive was configured (SetKeepAlivePeriod) but never actually
enabled (SO_KEEPALIVE) on accepted client connections. Go 1.26's
SetKeepAlivePeriod only sets TCP_KEEPIDLE — it does not call
setsockopt(SO_KEEPALIVE, 1). Without SO_KEEPALIVE the kernel never
sends probe packets, so dead connections from sleeping mobile clients
linger until the idle timeout fires.

Replace SetKeepAlive + SetKeepAlivePeriod with net.KeepAliveConfig
(available since Go 1.24) for explicit per-socket control:

  Idle:     30s   (time before first probe)
  Interval: 10s   (between probes)
  Count:    3     (failed probes to declare dead)

This detects dead connections in ~60s instead of relying on system
defaults (tcp_keepalive_intvl=75s, probes=9 → up to 11 minutes).

Increase the default idle timeout from 1 minute to 5 minutes.
MTProto clients send ping_delay_disconnect every ~60s, which resets
the idle timer. The previous 1-minute default created a race: if a
ping arrived even 1–2 seconds late the relay was killed. A 5-minute
window also survives typical mobile sleep periods (phone idle 2–5 min)
where the NAT mapping is still alive and the connection can resume
without reconnection.

Cherry-picked from 9seconds/mtg@5f81ae3 with fork-specific fixes:
- keep "time" import in run_proxy.go (used by throttle feature)
- fix network/sockopts_test.go import path to dolonet/mtg-multi

When total connections exceed a configurable limit, a background
goroutine (every 5s by default) computes per-user caps using a
fair-share algorithm: small users keep their connections, remaining
budget is split equally among heavy users. New connections from
over-cap users are rejected; existing connections are not killed.

Config:
  [throttle]
  max-connections = 5000
  check-interval = "5s"

Stats API response now includes throttle state with active caps.

DPI bypass tools like ByeDPI fragment a single TLS record into multiple
records to evade censorship. This broke ReadClientHello because it
assumed the entire ClientHello arrives in one TLS record.

Add reassembleTLSHandshake that reads continuation records and
reconstructs a single TLS record before parsing and HMAC verification.
Per RFC 5246 Section 6.2.1, handshake messages may be fragmented
across multiple records — this is valid TLS behavior.

go install github.com/dolonet/mtg-multi@latest was broken because go.mod
declared module path as github.com/9seconds/mtg/v2 while the repo lives
at github.com/dolonet/mtg-multi. Users ended up installing upstream
binary without multi-secret support.

Fixes https://github.com/9seconds/mtg/issues/376#issuecomment-4162877568

For a couple of releases we use collected IPs as a prioritized source
for connecting to Telegram. But apparently, they work way worse than it
should, and having connectivity to core ip ALWAYS gives better results.
Thus, this PR flips priorities, so users could have auto-update enabled
as a source of secondary addresses, not primary ones

- Replace manual make+copy with slices.Clone in Snapshot()
- Remove redundant _ = len(data); Snapshot() call alone is
  sufficient to exercise the lock under -race

- Move error check before Snapshot() to avoid unnecessary allocation
- Update existing tests to use Snapshot() instead of direct field access
- Add TestConcurrentAddSnapshot to explicitly exercise the mutex

1. Add sync.Mutex to ScoutConnCollected to eliminate data race between
   Add()/MarkWrite() in readLoop and learn() iterating results.
   Introduce Snapshot() for safe read access.

2. Increase bloom filter test size from 500 to 100000 to prevent
   false negatives from random eviction in the stable bloom filter.

3. Use Require().NoError() in TestHTTPSRequest to prevent nil-pointer
   panic on resp.Body.Close() when the request fails.

Fixes #425

Cover shared idle tracker behavior:
- tracker lifecycle (new, idle after timeout, touch resets)
- read/write with data touches tracker
- read retries on timeout when tracker is not idle
- read closes on timeout when tracker is idle
- shared tracker prevents false timeout across directions

connIdleTimeout previously set per-direction deadlines independently.
During media downloads the client→telegram direction can be idle at the
application level while telegram→client is actively streaming data.
After IdleTimeout (default 1 min) the idle direction's ReadDeadline
fires, tearing down the entire relay and breaking media transfers.

Replace the per-direction timeout with a shared atomic timestamp that
both pump goroutines update on any successful Read or Write. When a
ReadDeadline fires on the idle direction, we check the shared tracker:
if the other direction was recently active, we retry instead of closing.
The connection is only torn down when both directions are idle for the
full timeout period.

This matches the documented IdleTimeout contract: "if we have any
message which will pass to either direction, a timer is reset."

Overhead: one atomic.Int64 (8 bytes) per connection pair, one
atomic.Store (~1 ns) per Read/Write with data, zero extra goroutines.

Fixes #423

Wrap both sides of the Telegram relay in connIdleTimeout,
same as already done for domain fronting in #416.

Without this, if a client disappears (network drop, battery dies),
the TCP connection stays formally alive and the goroutine in the
worker pool blocks on io.CopyBuffer indefinitely. Under mass client
disconnects this accumulates zombie goroutines.

Fixes #417

This is a followup for https://github.com/9seconds/mtg/issues/412 it
makes sense to manage timers inplace instead of creating for new
goroutines: saves memory

Support multiple named secrets in [secrets] config section. During
FakeTLS handshake each secret is tried until HMAC validates. Matched
secret name is logged and used for per-user statistics tracking.

Built-in HTTP stats API (configurable via api-bind-to) exposes
GET /stats with per-user connection counts, bytes in/out, and
last-seen timestamps.

Backward compatible: single "secret" config key still works.

- avoid deprecated DefaultIdleTimeout, use time.Minute directly
- simplify embedded field selectors (QF1008)

When the worker pool rejected a connection (ErrPoolOverload), the
accepted net.Conn was never closed — leaking a file descriptor and
TCP socket per rejected connection. Under sustained traffic spikes this
compounds the problem: leaked descriptors reduce the capacity for new
dials (including to the fronting domain), accelerating the failure
cascade described in #378.

Domain fronting relay (for non-Telegram traffic) had no idle timeout,
causing worker pool exhaustion under traffic spikes.

The ProxyOpts.IdleTimeout field existed but was never wired into the
proxy. Now domain fronting connections are wrapped with per-read/write
deadlines reset to the configured idle timeout (default 1m), so stale
or slowloris-style connections are reaped promptly.

Fixes #378

- Use sync.Pool for relay buffers instead of stack-allocated arrays.
  A [16379]byte on the goroutine stack forces Go to grow it to 32KB
  (next power of two). Pooled buffers keep goroutine stacks small.

- Same fix for doppelganger write buffer ([16384]byte in conn.start).

- Replace idle goroutines with context.AfterFunc in proxy.ServeConn
  and relay.Relay. These goroutines existed only to wait on ctx.Done()
  and close connections. AfterFunc achieves the same without allocating
  a goroutine until the context is actually cancelled.

Net effect: at 3000 concurrent connections on a 1-vCPU/961MB VPS,
the unmodified binary drops 246 connections and falls to 10 MB/s.
With these changes: zero failures, 63 MB/s, 31% lower RSS.

Closes #412

Instead of a separate cert_probe.go that duplicates the scout's TLS
connection logic, measure the cert chain size directly from the same
HTTPS connections the scout already makes.

Changes:
- Extend ScoutConnResult with payloadLen field
- Add Write interception to ScoutConn for handshake boundary detection
- Scout.learn() now computes cert size (sum of ApplicationData between
  CCS and first client Write) alongside inter-record durations
- Ganger aggregates cert sizes across raids and exposes NoiseParams()
  via atomic pointer for lock-free reads from proxy goroutines
- Proxy reads NoiseParams from Ganger on each handshake instead of
  probing at startup
- Remove cert_probe.go, disk cache, and related config options
  (noise-cache-path, noise-cache-ttl, noise-probe-count)

Falls back to legacy 2500-4700 range until the first scout raid
completes (typically within 1-2 seconds of startup).

The hardcoded noise range (2500-4700 bytes) in the FakeTLS ServerHello
does not match the real certificate chain sizes of many popular fronting
domains (e.g., dl.google.com ≈ 6480 bytes, microsoft.com ≈ 13004 bytes).
This makes the proxy detectable by DPI systems that compare the
ApplicationData size with the real cert chain size for the SNI domain.

On startup, probe the fronting domain's actual TLS handshake size and
use the measured value ± jitter instead of the static range. Falls back
to the legacy 2500-4700 range if the probe fails.

Also adds optional caching of probe results between restarts
(noise-cache-path, noise-cache-ttl) and a configurable probe count
(noise-probe-count) under [defense.doppelganger].

Closes #408

Even if it makes sense to have a huge buffers, we do artificial delays
now. In that case we could achieve the same results with a lower buffer.
If not, then we won't send a packet bigger that this value