docs: add FAQ.md (merged mining, address autoconversion, payouts, dashboard)

README.md

@@ -116,6 +116,8 @@ Miners connect to stratum and set their LTC payout address as the username
 
 Full step-by-step guides: [Linux](doc/build-unix.md) | [macOS](doc/build-macos.md) | [Windows](doc/build-windows.md)
 
+Common operator questions (merged coins, payouts, dashboard): [docs/FAQ.md](docs/FAQ.md)
+
 ---
 
 ## Operating modes

docs/FAQ.md

@@ -0,0 +1,184 @@
+# c2pool FAQ
+
+Common questions from operators running `./c2pool`. See the
+[README](../README.md) for the full option reference and `./c2pool --help`
+for every flag.
+
+---
+
+## Merged mining
+
+### How do I add merged coins? Do I implement them in code, or is there a command?
+
+It's a **runtime command-line flag — no code changes**.
+
+- **LTC + DOGE are built in.** They run as **embedded SPV** nodes (no coin
+  daemon, no config). DOGE merged mining activates automatically — running
+  `./c2pool` with no arguments already merge-mines LTC + DOGE.
+
+- **Other aux chains** are added by running *their* daemon and passing
+  `--merged`:
+
+  ```bash
+  ./c2pool --merged PEP:63:127.0.0.1:29377:rpcuser:rpcpass
+  ```
+
+  Format: `COIN:chain_id:host:port:rpcuser:rpcpass`. c2pool drives the aux
+  daemon over its `createauxblock` / `submitauxblock` RPC. Repeat `--merged`
+  for multiple chains.
+
+| Coin  | chain_id | Backend                | Notes                              |
+|-------|----------|------------------------|------------------------------------|
+| DOGE  | 98       | **Embedded SPV**       | auto-configured, on by default     |
+| PEP   | 63       | External daemon        | `--merged PEP:63:host:port:user:pass`   |
+| BELLS | 16       | External daemon        | `--merged BELLS:16:host:port:user:pass` |
+| LKY   | 8211     | External daemon        | `--merged LKY:8211:host:port:user:pass` |
+| JKC   | 8224     | External daemon        | `--merged JKC:8224:host:port:user:pass` |
+| SHIC  | 74       | External daemon        | `--merged SHIC:74:host:port:user:pass`  |
+
+Only **LTC and DOGE** are daemonless (embedded SPV). Every other aux chain
+needs its own full node running locally with AuxPoW RPC
+(`createauxblock`/`submitauxblock`) enabled.
+
+---
+
+### Can I merge-mine DigiByte (DGB)? Is DigiByte "SPV" now?
+
+**No — DGB cannot be merge-mined as a child of LTC, and it is not an embedded
+SPV coin today.**
+
+DigiByte does **not** support AuxPoW (auxiliary proof-of-work) and has **no
+AuxPoW chain ID**. Unlike Dogecoin (chain_id 98) or Namecoin (chain_id 1),
+which are child chains that inherit security from a parent's hashrate, DigiByte
+secures its own chain directly through a **MultiAlgo** consensus: five
+independent proof-of-work algorithms — **Scrypt, SHA-256d, Qubit, Skein, and
+Odocrypt** — each mined directly on the DGB main chain with its own independent
+difficulty adjustment. Because DGB is a primary chain with no aux-chain role, it
+is **not** a valid `--merged` target. The `--merged` flag is only for true
+AuxPoW coins (DOGE, PEP, BELLS, LKY, JKC, SHIC).
+
+In c2pool, DGB-Scrypt is therefore handled as its **own parent chain** — a
+standalone DGB-Scrypt P2Pool node running its own sharechain (Scrypt-only in
+V36; the other four DGB algos are out of scope for now). That parent-chain
+support is **in development** (`--net digibyte`), not yet in the stable LTC
+release. Until it ships there is no LTC-side path to mine DGB through c2pool.
+
+---
+
+## Payouts & funds
+
+### Where does it mine to when using SPV? How do I access the funds?
+
+**c2pool holds no wallet and never custodies coins.** The embedded SPV nodes
+are header-only — they validate the chain but store no keys. Block rewards are
+paid **directly in the block's coinbase** to an address **you** control in your
+own wallet (Litecoin Core, Dogecoin Core, etc.). There is nothing to "withdraw"
+from c2pool — the coins land in your address the moment a block matures.
+
+You set your payout address as your **stratum username** (the P2Pool
+convention):
+
+```
+LcYourLitecoinAddress.worker1
+```
+
+**You normally supply just one address.** c2pool **auto-derives** the payout
+address for every merged chain from that single primary address — LTC, DOGE and
+the other Scrypt aux chains all share the same secp256k1 keys, so the same
+`hash160` is re-encoded into each chain's address format automatically. Give
+your LTC address and your DOGE reward is paid to the matching DOGE address with
+no extra configuration.
+
+**This auto-conversion is conditional on your address type:**
+
+| Primary address type | Merged payout auto-derived? |
+|----------------------|-----------------------------|
+| P2PKH  (`L...`, legacy)      | ✅ yes |
+| P2SH   (`M...` / `3...`)     | ✅ yes |
+| P2WPKH (`ltc1q...`, segwit)  | ✅ yes |
+| P2WSH  (`ltc1q...`, 32-byte) | ❌ no — supply merged addresses explicitly |
+| P2TR   (`ltc1p...`, taproot) | ❌ no — supply merged addresses explicitly |
+
+The 32-byte witness programs (P2WSH/P2TR) can't be reduced to a 20-byte
+`hash160`, so for those you must name each chain's address yourself.
+
+**To override or set addresses per chain explicitly**, use any of:
+
+- **Slash + chain_id** (most explicit):
+  `LTCADDR/98:DOGEADDR` — pays DOGE (chain_id 98) to `DOGEADDR`.
+  Chain multiple: `LTCADDR/98:DOGEADDR/63:PEPADDR`.
+- **Simple separator** (`,` `|` `;` or space): `LTCADDR,DOGEADDR` — first is
+  the parent (LTC), second is the merged child.
+- **Stratum method**: send `mining.set_merged_addresses`.
+
+c2pool also **auto-corrects a swapped order** (if it detects the merged-chain
+address first and the LTC address second) and, if you enter a DOGE address as
+the primary, **reverse-derives** the LTC payout from the same key.
+
+Worker names (`.worker1` or `_worker1`) are stripped from each address before
+use.
+
+### Which mode pays whom?
+
+| Mode | CLI flag | Who gets paid |
+|------|----------|---------------|
+| **Integrated** (default) | *(none)* | All miners in the PPLNS window, by sharechain weight — paid to each miner's stratum-username address |
+| **Solo** | `--solo` | Your connected miners, proportional to hashrate — paid to their addresses |
+| **Custodial** | `--custodial --address ADDR` | **100% to the operator's `--address`**; miners are tracked off-chain via `/stratum_stats` |
+
+In integrated and solo modes the miner's address appears **directly in the
+coinbase** — the pool never holds the funds. Only `--custodial` routes
+everything to the operator for off-chain accounting.
+
+---
+
+## Dashboard & explorer
+
+### How do I add the dashboard? The docs don't have the integration files anymore.
+
+**The dashboard is built in — there is nothing to install.** Whenever c2pool
+runs (integrated, solo, or custodial mode), it serves the web dashboard and
+REST API automatically:
+
+```
+http://localhost:8080/
+```
+
+Just open that URL in a browser. Change the port with `--web-port PORT`
+(`web_port:` in YAML). The dashboard files live in `web-static/` and are
+fully user-customizable — edit the HTML/JS/CSS there to restyle it.
+
+**Optional lite block explorer** — a separate bundled Python app for browsing
+recent blocks, decoded coinbase scripts, and THE commitment proofs:
+
+```yaml
+# in your config
+explorer: true
+explorer_url: "http://localhost:9090"
+```
+
+```bash
+python3 explorer/explorer.py \
+  --ltc-c2pool http://127.0.0.1:8080/api/explorer \
+  --web-port 9090
+```
+
+Then browse `http://localhost:9090/`.
+
+> **Note:** the README currently links `docs/DASHBOARD_INTEGRATION.md` for the
+> full REST API reference, but that file is missing from the tree — tracked in
+> [#677](https://github.com/frstrtr/c2pool/issues/677). The API endpoints
+> themselves work and are listed in the README's API table; the dashboard is
+> served automatically as described above.
+
+---
+
+## Ports (defaults)
+
+| Port  | Purpose                          | Override         |
+|-------|----------------------------------|------------------|
+| 9326  | P2Pool sharechain (peer-to-peer) | `--p2pool-port`  |
+| 9327  | Stratum mining                   | `-w PORT`        |
+| 8080  | Web dashboard + REST API         | `--web-port`     |
+
+On `--testnet`, P2P shifts to 19326 and stratum to 19327.