chancloser: update RBF close documentation for taproot support

diff --git a/lnwallet/chancloser/rbf_close.md b/lnwallet/chancloser/rbf_close.md
index ac532c5..0a149a7 100644
--- a/lnwallet/chancloser/rbf_close.md
+++ b/lnwallet/chancloser/rbf_close.md
@@ -178,6 +178,35 @@ The `CloseErr` state provides recovery paths when protocol violations occur:
 
 Recovery typically involves restarting the negotiation with a new closing offer.
 
+### RBF Nonce Flow Example
+
+Here's how nonces flow through an RBF cooperative close with taproot:
+
+1. **Initial Shutdown**:
+   - Alice sends `shutdown` with her closee nonce `NA`
+   - Bob sends `shutdown` with his closee nonce `NB`
+
+2. **First Close Attempt** (Alice as closer):
+   - Alice sends `closing_complete`:
+     - Uses Bob's nonce NB (from shutdown) to create her closer signature
+     - Includes `PartialSigWithNonce` with her next closee nonce `NA2`
+   - Bob sends `closing_sig`:
+     - Uses Alice's nonce NA (from shutdown) to create his closee signature
+     - Includes `NextCloseeNonce` with his next closee nonce `NB2`
+
+3. **RBF Iteration** (Bob as closer):
+   - Bob sends `closing_complete`:
+     - Uses Alice's nonce NA2 (from previous `PartialSigWithNonce`) to create
+       his closer signature
+     - Includes `PartialSigWithNonce` with his next closee nonce `NB3`
+   - Alice sends `closing_sig`:
+     - Uses Bob's nonce NB2 (from previous `NextCloseeNonce`) to create her
+       closee signature
+     - Includes `NextCloseeNonce` with her next closee nonce `NA3`
+
+The pattern continues with each party using the nonce they received in the
+previous round.
+
 ## Example Scenarios
 
 ### Standard Cooperative Close
@@ -211,9 +240,103 @@ Recovery typically involves restarting the negotiation with a new closing offer.
 5. When agreement is reached on new fees: `ClosePending` → `CloseFin` (via
    `txn_confirmation`)
 
+## Taproot Channel Support
+
+### MuSig2 Nonce Handling
+
+For taproot channels, the cooperative close process requires coordination for
+MuSig2 signature creation using a JIT (Just-In-Time) nonce pattern:
+
+#### Nonce Exchange During Shutdown
+
+For taproot channels using the modern RBF cooperative close flow:
+- The `shutdown` message includes a single nonce field:
+  - `shutdown_nonce` (TLV type 8): The sender's "closee nonce" used when they
+  send `closing_sig`
+- This simplified approach works because nonces are sent JIT with signatures
+
+#### JIT (Just-In-Time) Nonce Pattern
+
+The protocol uses an asymmetric signature pattern for taproot channels that
+optimizes nonce delivery:
+
+**Asymmetric Roles**:
+- **Closer**: The party proposing a fee (sends `closing_complete`)
+- **Closee**: The party accepting the fee (sends `closing_sig`)
+
+**ClosingComplete (from Closer)**:
+- Uses `PartialSigWithNonce` (98 bytes total):
+  - The partial signature (32 bytes)
+  - The sender's next closee nonce (66 bytes)
+- Bundles the nonce because the closee hasn't seen it yet
+- TLV types 5, 6, 7 (distinct from non-taproot types 1, 2, 3)
+
+**ClosingSig (from Closee)**:
+- Uses `PartialSig` (32 bytes) + separate `NextCloseeNonce`:
+  - The partial signature in TLV types 5, 6, 7
+  - The next closee nonce in TLV type 22 (66 bytes)
+- Separates the nonce because the closer already knows the current nonce from
+  shutdown or previous `PartialSigWithNonce`
+
+This asymmetric pattern minimizes redundancy while ensuring both parties always
+have the nonces they need for signing.
+
+#### Nonce State Management
+
+The state machine maintains a simplified `NonceState` structure with only 2 fields:
+- `LocalCloseeNonce`: Our closee nonce sent in our shutdown message
+- `RemoteCloseeNonce`: The peer's closee nonce from their shutdown message
+
+The JIT pattern eliminates complex nonce rotation:
+- New nonces arrive with signatures, not pre-generated
+- Remote nonces are updated automatically from `PartialSigWithNonce` in
+  `closing_complete`
+- Local nonces are generated on-demand when creating signatures
+
+### Wire Message Extensions
+
+The following messages have been extended with optional TLV fields for taproot:
+
+**shutdown**:
+- Type 8: `shutdown_nonce` - Sender's closee nonce for cooperative close signing
+
+**closing_complete**:
+- Types 5, 6, 7: `PartialSigWithNonce` - Partial signature with embedded next closee nonce
+  - Type 5: `closer_no_closee` (closer has output, closee is dust)
+  - Type 6: `no_closer_closee` (closer is dust, closee has output)
+  - Type 7: `closer_and_closee` (both have outputs)
+
+**closing_sig**:
+- Types 5, 6, 7: `PartialSig` - Just the partial signature (32 bytes)
+  - Same TLV type meanings as above
+- Type 22: `NextCloseeNonce` - Next closee nonce for RBF iterations (66 bytes)
+
+### Validation Requirements
+
+For taproot channels:
+- Shutdown messages MUST include the sender's closee nonce
+- ClosingComplete messages MUST use PartialSigWithNonce (includes next nonce
+  bundled with signature)
+- ClosingSig messages MUST use PartialSig with separate NextCloseeNonce field
+- Terminal offers (final RBF attempts) MAY omit next nonces to signal finality
+
+### Implementation Notes for Nonce Handling
+
+The MuSig2 session's `InitRemoteNonce` method is called at two specific times:
+1. When processing the remote's `shutdown` message (to initialize with their
+   closee nonce)
+
+2. After receiving a `closing_sig` message that contains a `NextCloseeNonce`
+   (for RBF iterations)
+
+The nonce from `PartialSigWithNonce` in `closing_complete` is stored but not
+immediately used with `InitRemoteNonce` - it's used when we need to sign as the
+closee in the next round.
+
 ## Implementation Notes
 
 - This state machine is implemented in the `peer.go` and `channel.go` files
 within the lnd codebase
 - State transitions are logged at the debug level
 - The `ChanCloser` interface manages the state machine execution
+- Taproot support requires the `MusigSession` interface for nonce coordination