feat(chain): remove channels, add social feed (Phase A of v2.0.0)

Replaces the channel/membership model with a VK/Twitter-style feed:
public posts, follow graph, likes. Views are deliberately off-chain
(counted by the hosting relay, Phase B).

Removed
  - EventCreateChannel, EventAddMember
  - CreateChannelPayload, AddMemberPayload, ChannelMember
  - prefixChannel, prefixChanMember
  - chain.Channel(), chain.ChannelMembers()
  - node/api_channels.go
  - GetChannel, GetChannelMembers on ExplorerQuery

Added
  - Events: CREATE_POST, DELETE_POST, FOLLOW, UNFOLLOW, LIKE_POST, UNLIKE_POST
  - Payloads: CreatePostPayload, DeletePostPayload, FollowPayload,
    UnfollowPayload, LikePostPayload, UnlikePostPayload
  - Stored shape: PostRecord (author, size, hash, hosting relay, timestamp,
    reply/quote refs, soft-delete flag, fee paid)
  - State prefixes: post:, postbyauthor:, follow:, followin:, like:, likecount:
  - Queries: Post(), PostsByAuthor(), Following(), Followers(),
    LikeCount(), HasLiked()
  - Cached like counter via bumpLikeCount helper

Pricing
  - BasePostFee = 1000 µT (aligned with MinFee block-validation floor)
  - PostByteFee = 1 µT/byte of compressed content
  - Total fee credited in full to HostingRelay pub (storage compensation)
  - MaxPostSize = 256 KiB

Integrity
  - CREATE_POST validates content_hash length (32 B) and size range
  - DELETE_POST restricted to post.Author
  - Duplicate FOLLOW / LIKE rejected
  - reply_to and quote_of mutually exclusive

Tests
  - TestFeedCreatePost: post stored, indexed, host credited
  - TestFeedInsufficientFee: underpaid post is skipped
  - TestFeedFollowUnfollow: follow graph round-trips via forward + inbound indices
  - TestFeedLikeUnlike: like toggles with dedup, counter stays accurate
  - TestFeedDeletePostByOther: non-author deletion rejected

This is Phase A (chain-layer). Phase B adds the relay feed-mailbox
(post bodies + gossipsub) and HTTP endpoints. Phase C adds the client
Feed tab.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

blockchain/chain.go

@@ -40,8 +40,14 @@ const (
 	prefixHeight        = "height"          // height → uint64
 	prefixBalance       = "balance:"        // balance:<pubkey> → uint64
 	prefixIdentity      = "id:"             // id:<pubkey> → RegisterKeyPayload JSON
-	prefixChannel       = "chan:"           // chan:<channelID> → CreateChannelPayload JSON
-	prefixChanMember    = "chan-member:"    // chan-member:<channelID>:<memberPubKey> → "" (presence = member)
+
+	// Social feed (v2.0.0). Replaced the old channel keys (chan:, chan-member:).
+	prefixPost         = "post:"           // post:<postID> → PostRecord JSON
+	prefixPostByAuthor = "postbyauthor:"   // postbyauthor:<author>:<ts_20d>:<postID> → "" (chrono index)
+	prefixFollow       = "follow:"         // follow:<follower>:<target> → "" (presence = follows)
+	prefixFollowInbound = "followin:"      // followin:<target>:<follower> → "" (reverse index — counts followers)
+	prefixLike         = "like:"           // like:<postID>:<liker> → "" (presence = liked)
+	prefixLikeCount    = "likecount:"      // likecount:<postID> → uint64 (cached count)
 	prefixWalletBind    = "walletbind:"    // walletbind:<node_pubkey> → wallet_pubkey (string)
 	prefixReputation    = "rep:"           // rep:<pubkey> → RepStats JSON
 	prefixPayChan       = "paychan:"       // paychan:<channelID> → PayChanState JSON
@@ -538,11 +544,13 @@ func (c *Chain) Identity(pubKeyHex string) (*RegisterKeyPayload, error) {
 	return &p, err
 }
 
-// Channel returns the CreateChannelPayload for a channel ID, or nil.
-func (c *Chain) Channel(channelID string) (*CreateChannelPayload, error) {
-	var p CreateChannelPayload
+// ── Feed queries (v2.0.0) ──────────────────────────────────────────────────
+
+// Post returns the PostRecord for a post ID, or nil if not found.
+func (c *Chain) Post(postID string) (*PostRecord, error) {
+	var p PostRecord
 	err := c.db.View(func(txn *badger.Txn) error {
-		item, err := txn.Get([]byte(prefixChannel + channelID))
+		item, err := txn.Get([]byte(prefixPost + postID))
 		if err != nil {
 			return err
 		}
@@ -553,13 +561,62 @@ func (c *Chain) Channel(channelID string) (*CreateChannelPayload, error) {
 	if errors.Is(err, badger.ErrKeyNotFound) {
 		return nil, nil
 	}
-	return &p, err
+	if err != nil {
+		return nil, err
+	}
+	return &p, nil
 }
 
-// ChannelMembers returns the public keys of all members added to channelID.
-func (c *Chain) ChannelMembers(channelID string) ([]string, error) {
-	prefix := []byte(fmt.Sprintf("%s%s:", prefixChanMember, channelID))
-	var members []string
+// PostsByAuthor returns the last `limit` posts by the given author, newest
+// first. Iterates `postbyauthor:<author>:...` in reverse order. If limit
+// ≤ 0, defaults to 50; capped at 200.
+func (c *Chain) PostsByAuthor(authorPub string, limit int) ([]*PostRecord, error) {
+	if limit <= 0 {
+		limit = 50
+	}
+	if limit > 200 {
+		limit = 200
+	}
+	prefix := []byte(prefixPostByAuthor + authorPub + ":")
+	var out []*PostRecord
+
+	err := c.db.View(func(txn *badger.Txn) error {
+		opts := badger.DefaultIteratorOptions
+		opts.Prefix = prefix
+		opts.Reverse = true // newest (higher ts) first — reverse iteration
+		opts.PrefetchValues = false
+		// For reverse iteration Badger requires seeking past the prefix range.
+		seek := append([]byte{}, prefix...)
+		seek = append(seek, 0xff)
+
+		it := txn.NewIterator(opts)
+		defer it.Close()
+		for it.Seek(seek); it.ValidForPrefix(prefix) && len(out) < limit; it.Next() {
+			key := string(it.Item().Key())
+			// key = "postbyauthor:<author>:<ts_20d>:<postID>"
+			parts := strings.Split(key, ":")
+			if len(parts) < 4 {
+				continue
+			}
+			postID := parts[len(parts)-1]
+			rec, err := c.postInTxn(txn, postID)
+			if err != nil || rec == nil {
+				continue
+			}
+			if rec.Deleted {
+				continue
+			}
+			out = append(out, rec)
+		}
+		return nil
+	})
+	return out, err
+}
+
+// Following returns the Ed25519 pubkeys that `follower` subscribes to.
+func (c *Chain) Following(followerPub string) ([]string, error) {
+	prefix := []byte(prefixFollow + followerPub + ":")
+	var out []string
 	err := c.db.View(func(txn *badger.Txn) error {
 		opts := badger.DefaultIteratorOptions
 		opts.PrefetchValues = false
@@ -568,15 +625,95 @@ func (c *Chain) ChannelMembers(channelID string) ([]string, error) {
 		defer it.Close()
 		for it.Rewind(); it.Valid(); it.Next() {
 			key := string(it.Item().Key())
-			// key = "chan-member:<channelID>:<memberPubKey>"
+			// key = "follow:<follower>:<target>"
 			parts := strings.SplitN(key, ":", 3)
 			if len(parts) == 3 {
-				members = append(members, parts[2])
+				out = append(out, parts[2])
 			}
 		}
 		return nil
 	})
-	return members, err
+	return out, err
+}
+
+// Followers returns the Ed25519 pubkeys that follow `target`.
+func (c *Chain) Followers(targetPub string) ([]string, error) {
+	prefix := []byte(prefixFollowInbound + targetPub + ":")
+	var out []string
+	err := c.db.View(func(txn *badger.Txn) error {
+		opts := badger.DefaultIteratorOptions
+		opts.PrefetchValues = false
+		opts.Prefix = prefix
+		it := txn.NewIterator(opts)
+		defer it.Close()
+		for it.Rewind(); it.Valid(); it.Next() {
+			key := string(it.Item().Key())
+			parts := strings.SplitN(key, ":", 3)
+			if len(parts) == 3 {
+				out = append(out, parts[2])
+			}
+		}
+		return nil
+	})
+	return out, err
+}
+
+// LikeCount returns the cached count of likes for a post (O(1)).
+func (c *Chain) LikeCount(postID string) (uint64, error) {
+	var count uint64
+	err := c.db.View(func(txn *badger.Txn) error {
+		item, err := txn.Get([]byte(prefixLikeCount + postID))
+		if errors.Is(err, badger.ErrKeyNotFound) {
+			return nil
+		}
+		if err != nil {
+			return err
+		}
+		return item.Value(func(val []byte) error {
+			if len(val) == 8 {
+				count = binary.BigEndian.Uint64(val)
+			}
+			return nil
+		})
+	})
+	return count, err
+}
+
+// HasLiked reports whether `liker` has liked the given post.
+func (c *Chain) HasLiked(postID, likerPub string) (bool, error) {
+	key := []byte(prefixLike + postID + ":" + likerPub)
+	var ok bool
+	err := c.db.View(func(txn *badger.Txn) error {
+		_, err := txn.Get(key)
+		if err == nil {
+			ok = true
+			return nil
+		}
+		if errors.Is(err, badger.ErrKeyNotFound) {
+			return nil
+		}
+		return err
+	})
+	return ok, err
+}
+
+// postInTxn is the internal helper used by iteration paths to fetch a full
+// PostRecord without opening a new View transaction.
+func (c *Chain) postInTxn(txn *badger.Txn, postID string) (*PostRecord, error) {
+	item, err := txn.Get([]byte(prefixPost + postID))
+	if errors.Is(err, badger.ErrKeyNotFound) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	var p PostRecord
+	if err := item.Value(func(val []byte) error {
+		return json.Unmarshal(val, &p)
+	}); err != nil {
+		return nil, err
+	}
+	return &p, nil
 }
 
 // WalletBinding returns the payout wallet pub key bound to a node, or "" if none.
@@ -741,41 +878,197 @@ func (c *Chain) applyTx(txn *badger.Txn, tx *Transaction) (uint64, error) {
 			return 0, err
 		}
 
-	case EventCreateChannel:
-		var p CreateChannelPayload
+	// ── Feed events (v2.0.0) ──────────────────────────────────────────
+	case EventCreatePost:
+		var p CreatePostPayload
 		if err := json.Unmarshal(tx.Payload, &p); err != nil {
-			return 0, fmt.Errorf("%w: CREATE_CHANNEL bad payload: %v", ErrTxFailed, err)
+			return 0, fmt.Errorf("%w: CREATE_POST bad payload: %v", ErrTxFailed, err)
+		}
+		if p.PostID == "" {
+			return 0, fmt.Errorf("%w: CREATE_POST: post_id required", ErrTxFailed)
+		}
+		if len(p.ContentHash) != 32 {
+			return 0, fmt.Errorf("%w: CREATE_POST: content_hash must be 32 bytes", ErrTxFailed)
+		}
+		if p.HostingRelay == "" {
+			return 0, fmt.Errorf("%w: CREATE_POST: hosting_relay required", ErrTxFailed)
+		}
+		if p.Size == 0 || p.Size > MaxPostSize {
+			return 0, fmt.Errorf("%w: CREATE_POST: size %d out of range (0, %d]",
+				ErrTxFailed, p.Size, MaxPostSize)
+		}
+		if p.ReplyTo != "" && p.QuoteOf != "" {
+			return 0, fmt.Errorf("%w: CREATE_POST: reply_to and quote_of are mutually exclusive", ErrTxFailed)
+		}
+		// Duplicate check — same post_id may only commit once.
+		if _, err := txn.Get([]byte(prefixPost + p.PostID)); err == nil {
+			return 0, fmt.Errorf("%w: CREATE_POST: post %s already exists", ErrTxFailed, p.PostID)
+		}
+		// Fee formula: BasePostFee + size × PostByteFee. tx.Fee carries the
+		// full amount; we validate it matches and the sender can afford it.
+		expectedFee := BasePostFee + p.Size*PostByteFee
+		if tx.Fee < expectedFee {
+			return 0, fmt.Errorf("%w: CREATE_POST: fee %d < required %d (base %d + %d × %d bytes)",
+				ErrTxFailed, tx.Fee, expectedFee, BasePostFee, PostByteFee, p.Size)
 		}
 		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
-			return 0, fmt.Errorf("CREATE_CHANNEL debit: %w", err)
+			return 0, fmt.Errorf("CREATE_POST debit: %w", err)
 		}
-		val, _ := json.Marshal(p)
-		if err := txn.Set([]byte(prefixChannel+p.ChannelID), val); err != nil {
+		// Full fee goes to the hosting relay (storage compensation). No
+		// validator cut on posts — validators earn from other tx types. This
+		// incentivises nodes to actually host posts.
+		relayTarget, err := c.resolveRewardTarget(txn, p.HostingRelay)
+		if err != nil {
+			return 0, err
+		}
+		if err := c.creditBalance(txn, relayTarget, tx.Fee); err != nil {
+			return 0, fmt.Errorf("credit hosting relay: %w", err)
+		}
+		rec := PostRecord{
+			PostID:       p.PostID,
+			Author:       tx.From,
+			ContentHash:  p.ContentHash,
+			Size:         p.Size,
+			HostingRelay: p.HostingRelay,
+			ReplyTo:      p.ReplyTo,
+			QuoteOf:      p.QuoteOf,
+			CreatedAt:    tx.Timestamp.Unix(),
+			FeeUT:        tx.Fee,
+		}
+		recBytes, _ := json.Marshal(rec)
+		if err := txn.Set([]byte(prefixPost+p.PostID), recBytes); err != nil {
+			return 0, err
+		}
+		// Chrono index — allows PostsByAuthor to list newest-first in O(N).
+		idxKey := fmt.Sprintf("%s%s:%020d:%s", prefixPostByAuthor, tx.From, rec.CreatedAt, p.PostID)
+		if err := txn.Set([]byte(idxKey), []byte{}); err != nil {
 			return 0, err
 		}
 
-	case EventAddMember:
-		var p AddMemberPayload
+	case EventDeletePost:
+		var p DeletePostPayload
 		if err := json.Unmarshal(tx.Payload, &p); err != nil {
-			return 0, fmt.Errorf("%w: ADD_MEMBER bad payload: %v", ErrTxFailed, err)
+			return 0, fmt.Errorf("%w: DELETE_POST bad payload: %v", ErrTxFailed, err)
 		}
-		if p.ChannelID == "" {
-			return 0, fmt.Errorf("%w: ADD_MEMBER: channel_id required", ErrTxFailed)
+		if p.PostID == "" {
+			return 0, fmt.Errorf("%w: DELETE_POST: post_id required", ErrTxFailed)
 		}
-		if _, err := txn.Get([]byte(prefixChannel + p.ChannelID)); err != nil {
+		item, err := txn.Get([]byte(prefixPost + p.PostID))
+		if errors.Is(err, badger.ErrKeyNotFound) {
+			return 0, fmt.Errorf("%w: DELETE_POST: post %s not found", ErrTxFailed, p.PostID)
+		}
+		if err != nil {
+			return 0, err
+		}
+		var rec PostRecord
+		if err := item.Value(func(val []byte) error { return json.Unmarshal(val, &rec) }); err != nil {
+			return 0, err
+		}
+		if rec.Author != tx.From {
+			return 0, fmt.Errorf("%w: DELETE_POST: only author can delete", ErrTxFailed)
+		}
+		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
+			return 0, fmt.Errorf("DELETE_POST debit: %w", err)
+		}
+		rec.Deleted = true
+		val, _ := json.Marshal(rec)
+		if err := txn.Set([]byte(prefixPost+p.PostID), val); err != nil {
+			return 0, err
+		}
+
+	case EventFollow:
+		if tx.To == "" {
+			return 0, fmt.Errorf("%w: FOLLOW: target (to) is required", ErrTxFailed)
+		}
+		if tx.To == tx.From {
+			return 0, fmt.Errorf("%w: FOLLOW: cannot follow yourself", ErrTxFailed)
+		}
+		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
+			return 0, fmt.Errorf("FOLLOW debit: %w", err)
+		}
+		// follow:<follower>:<target> + reverse index followin:<target>:<follower>
+		fKey := []byte(prefixFollow + tx.From + ":" + tx.To)
+		if _, err := txn.Get(fKey); err == nil {
+			return 0, fmt.Errorf("%w: FOLLOW: already following", ErrTxFailed)
+		}
+		if err := txn.Set(fKey, []byte{}); err != nil {
+			return 0, err
+		}
+		if err := txn.Set([]byte(prefixFollowInbound+tx.To+":"+tx.From), []byte{}); err != nil {
+			return 0, err
+		}
+
+	case EventUnfollow:
+		if tx.To == "" {
+			return 0, fmt.Errorf("%w: UNFOLLOW: target (to) is required", ErrTxFailed)
+		}
+		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
+			return 0, fmt.Errorf("UNFOLLOW debit: %w", err)
+		}
+		fKey := []byte(prefixFollow + tx.From + ":" + tx.To)
+		if _, err := txn.Get(fKey); err != nil {
 			if errors.Is(err, badger.ErrKeyNotFound) {
-				return 0, fmt.Errorf("%w: ADD_MEMBER: channel %q not found", ErrTxFailed, p.ChannelID)
+				return 0, fmt.Errorf("%w: UNFOLLOW: not following", ErrTxFailed)
+			}
+			return 0, err
+		}
+		if err := txn.Delete(fKey); err != nil {
+			return 0, err
+		}
+		if err := txn.Delete([]byte(prefixFollowInbound + tx.To + ":" + tx.From)); err != nil {
+			return 0, err
+		}
+
+	case EventLikePost:
+		var p LikePostPayload
+		if err := json.Unmarshal(tx.Payload, &p); err != nil {
+			return 0, fmt.Errorf("%w: LIKE_POST bad payload: %v", ErrTxFailed, err)
+		}
+		if p.PostID == "" {
+			return 0, fmt.Errorf("%w: LIKE_POST: post_id required", ErrTxFailed)
+		}
+		if _, err := txn.Get([]byte(prefixPost + p.PostID)); err != nil {
+			if errors.Is(err, badger.ErrKeyNotFound) {
+				return 0, fmt.Errorf("%w: LIKE_POST: post %s not found", ErrTxFailed, p.PostID)
+			}
+			return 0, err
+		}
+		lKey := []byte(prefixLike + p.PostID + ":" + tx.From)
+		if _, err := txn.Get(lKey); err == nil {
+			return 0, fmt.Errorf("%w: LIKE_POST: already liked", ErrTxFailed)
+		}
+		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
+			return 0, fmt.Errorf("LIKE_POST debit: %w", err)
+		}
+		if err := txn.Set(lKey, []byte{}); err != nil {
+			return 0, err
+		}
+		if err := bumpLikeCount(txn, p.PostID, +1); err != nil {
+			return 0, err
+		}
+
+	case EventUnlikePost:
+		var p UnlikePostPayload
+		if err := json.Unmarshal(tx.Payload, &p); err != nil {
+			return 0, fmt.Errorf("%w: UNLIKE_POST bad payload: %v", ErrTxFailed, err)
+		}
+		if p.PostID == "" {
+			return 0, fmt.Errorf("%w: UNLIKE_POST: post_id required", ErrTxFailed)
+		}
+		lKey := []byte(prefixLike + p.PostID + ":" + tx.From)
+		if _, err := txn.Get(lKey); err != nil {
+			if errors.Is(err, badger.ErrKeyNotFound) {
+				return 0, fmt.Errorf("%w: UNLIKE_POST: not liked", ErrTxFailed)
 			}
 			return 0, err
 		}
 		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
-			return 0, fmt.Errorf("ADD_MEMBER debit: %w", err)
+			return 0, fmt.Errorf("UNLIKE_POST debit: %w", err)
 		}
-		member := tx.To
-		if member == "" {
-			member = tx.From
+		if err := txn.Delete(lKey); err != nil {
+			return 0, err
 		}
-		if err := txn.Set([]byte(fmt.Sprintf("%s%s:%s", prefixChanMember, p.ChannelID, member)), []byte{}); err != nil {
+		if err := bumpLikeCount(txn, p.PostID, -1); err != nil {
 			return 0, err
 		}
 
@@ -2336,6 +2629,35 @@ func (c *Chain) isValidatorTxn(txn *badger.Txn, pubKey string) (bool, error) {
 
 // verifyEd25519 verifies an Ed25519 signature without importing the identity package
 // (which would create a circular dependency).
+// bumpLikeCount adjusts the cached like counter for a post. delta = ±1.
+// Clamps at zero so a corrupt unlike without prior like can't underflow.
+func bumpLikeCount(txn *badger.Txn, postID string, delta int64) error {
+	key := []byte(prefixLikeCount + postID)
+	var cur uint64
+	item, err := txn.Get(key)
+	if err == nil {
+		if verr := item.Value(func(val []byte) error {
+			if len(val) == 8 {
+				cur = binary.BigEndian.Uint64(val)
+			}
+			return nil
+		}); verr != nil {
+			return verr
+		}
+	} else if !errors.Is(err, badger.ErrKeyNotFound) {
+		return err
+	}
+	switch {
+	case delta < 0 && cur > 0:
+		cur--
+	case delta > 0:
+		cur++
+	}
+	var buf [8]byte
+	binary.BigEndian.PutUint64(buf[:], cur)
+	return txn.Set(key, buf[:])
+}
+
 func verifyEd25519(pubKeyHex string, msg, sig []byte) (bool, error) {
 	pubBytes, err := hex.DecodeString(pubKeyHex)
 	if err != nil {

blockchain/chain_test.go

@@ -794,3 +794,248 @@ var _ = identity.Generate
 // Ensure ed25519 and hex are used directly (they may be used via helpers).
 var _ = ed25519.PublicKey(nil)
 var _ = hex.EncodeToString
+
+// ── Feed (v2.0.0) ──────────────────────────────────────────────────────────
+
+// TestFeedCreatePost: post commits, indexes, credits the hosting relay.
+func TestFeedCreatePost(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	alice := newIdentity(t) // post author
+	host := newIdentity(t)  // hosting relay pubkey
+
+	genesis := addGenesis(t, c, val)
+
+	// Fund alice + host.
+	const postSize = uint64(200)
+	expectedFee := blockchain.BasePostFee + postSize*blockchain.PostByteFee
+	fundAlice := makeTx(blockchain.EventTransfer, val.PubKeyHex(), alice.PubKeyHex(),
+		expectedFee+5*blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	time.Sleep(2 * time.Millisecond) // ensure distinct txID (nanosec clock)
+	fundHost := makeTx(blockchain.EventTransfer, val.PubKeyHex(), host.PubKeyHex(),
+		blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	b1 := buildBlock(t, genesis, val, []*blockchain.Transaction{fundAlice, fundHost})
+	mustAddBlock(t, c, b1)
+
+	hostBalBefore, _ := c.Balance(host.PubKeyHex())
+
+	h := sha256.Sum256([]byte("hello world post body"))
+	postPayload := blockchain.CreatePostPayload{
+		PostID:       "post1",
+		ContentHash:  h[:],
+		Size:         postSize,
+		HostingRelay: host.PubKeyHex(),
+	}
+	postTx := makeTx(
+		blockchain.EventCreatePost,
+		alice.PubKeyHex(), "",
+		0, expectedFee, // Fee = base + size*byte_fee; amount = 0
+		mustJSON(postPayload),
+	)
+	b2 := buildBlock(t, b1, val, []*blockchain.Transaction{postTx})
+	mustAddBlock(t, c, b2)
+
+	rec, err := c.Post("post1")
+	if err != nil || rec == nil {
+		t.Fatalf("Post(\"post1\") = %v, %v; want record", rec, err)
+	}
+	if rec.Author != alice.PubKeyHex() {
+		t.Errorf("author: got %q want %q", rec.Author, alice.PubKeyHex())
+	}
+	if rec.Size != postSize {
+		t.Errorf("size: got %d want %d", rec.Size, postSize)
+	}
+
+	// Host should have been credited the full fee.
+	hostBalAfter, _ := c.Balance(host.PubKeyHex())
+	if hostBalAfter != hostBalBefore+expectedFee {
+		t.Errorf("host balance: got %d, want %d (delta %d)",
+			hostBalAfter, hostBalBefore, expectedFee)
+	}
+
+	// PostsByAuthor should list it.
+	posts, err := c.PostsByAuthor(alice.PubKeyHex(), 10)
+	if err != nil {
+		t.Fatalf("PostsByAuthor: %v", err)
+	}
+	if len(posts) != 1 || posts[0].PostID != "post1" {
+		t.Errorf("PostsByAuthor: got %v, want [post1]", posts)
+	}
+}
+
+// TestFeedInsufficientFee: size-based fee is enforced.
+func TestFeedInsufficientFee(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	alice := newIdentity(t)
+	host := newIdentity(t)
+
+	genesis := addGenesis(t, c, val)
+	fundAlice := makeTx(blockchain.EventTransfer, val.PubKeyHex(), alice.PubKeyHex(),
+		10*blockchain.Token, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	b1 := buildBlock(t, genesis, val, []*blockchain.Transaction{fundAlice})
+	mustAddBlock(t, c, b1)
+
+	const postSize = uint64(1000)
+	h := sha256.Sum256([]byte("body"))
+	postPayload := blockchain.CreatePostPayload{
+		PostID:       "underpaid",
+		ContentHash:  h[:],
+		Size:         postSize,
+		HostingRelay: host.PubKeyHex(),
+	}
+	// Fee too low — base alone without the size component.
+	// (Must still be ≥ MinFee so the chain-level block validation passes;
+	// the per-event CREATE_POST check is what should reject it.)
+	postTx := makeTx(blockchain.EventCreatePost, alice.PubKeyHex(), "",
+		0, blockchain.MinFee, mustJSON(postPayload))
+	b2 := buildBlock(t, b1, val, []*blockchain.Transaction{postTx})
+	mustAddBlock(t, c, b2) // block commits, the tx is skipped (logged)
+
+	if rec, _ := c.Post("underpaid"); rec != nil {
+		t.Fatalf("post was stored despite insufficient fee: %+v", rec)
+	}
+}
+
+// TestFeedFollowUnfollow: follow graph round-trips via indices.
+func TestFeedFollowUnfollow(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	alice := newIdentity(t)
+	bob := newIdentity(t)
+
+	genesis := addGenesis(t, c, val)
+	fundAlice := makeTx(blockchain.EventTransfer, val.PubKeyHex(), alice.PubKeyHex(),
+		5*blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	b1 := buildBlock(t, genesis, val, []*blockchain.Transaction{fundAlice})
+	mustAddBlock(t, c, b1)
+
+	followTx := makeTx(blockchain.EventFollow, alice.PubKeyHex(), bob.PubKeyHex(),
+		0, blockchain.MinFee, mustJSON(blockchain.FollowPayload{}))
+	b2 := buildBlock(t, b1, val, []*blockchain.Transaction{followTx})
+	mustAddBlock(t, c, b2)
+
+	following, _ := c.Following(alice.PubKeyHex())
+	if len(following) != 1 || following[0] != bob.PubKeyHex() {
+		t.Errorf("Following: got %v, want [%s]", following, bob.PubKeyHex())
+	}
+	followers, _ := c.Followers(bob.PubKeyHex())
+	if len(followers) != 1 || followers[0] != alice.PubKeyHex() {
+		t.Errorf("Followers: got %v, want [%s]", followers, alice.PubKeyHex())
+	}
+
+	// Unfollow.
+	unfollowTx := makeTx(blockchain.EventUnfollow, alice.PubKeyHex(), bob.PubKeyHex(),
+		0, blockchain.MinFee, mustJSON(blockchain.UnfollowPayload{}))
+	b3 := buildBlock(t, b2, val, []*blockchain.Transaction{unfollowTx})
+	mustAddBlock(t, c, b3)
+
+	following, _ = c.Following(alice.PubKeyHex())
+	if len(following) != 0 {
+		t.Errorf("Following after unfollow: got %v, want []", following)
+	}
+}
+
+// TestFeedLikeUnlike: like toggles + cached count stays consistent.
+func TestFeedLikeUnlike(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	alice := newIdentity(t) // author
+	bob := newIdentity(t)   // liker
+	host := newIdentity(t)
+
+	genesis := addGenesis(t, c, val)
+
+	const postSize = uint64(100)
+	expectedPostFee := blockchain.BasePostFee + postSize*blockchain.PostByteFee
+	fundAlice := makeTx(blockchain.EventTransfer, val.PubKeyHex(), alice.PubKeyHex(),
+		expectedPostFee+5*blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	time.Sleep(2 * time.Millisecond)
+	fundBob := makeTx(blockchain.EventTransfer, val.PubKeyHex(), bob.PubKeyHex(),
+		5*blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	b1 := buildBlock(t, genesis, val, []*blockchain.Transaction{fundAlice, fundBob})
+	mustAddBlock(t, c, b1)
+
+	h := sha256.Sum256([]byte("likeable"))
+	postTx := makeTx(blockchain.EventCreatePost, alice.PubKeyHex(), "",
+		0, expectedPostFee,
+		mustJSON(blockchain.CreatePostPayload{
+			PostID: "p1", ContentHash: h[:], Size: postSize, HostingRelay: host.PubKeyHex(),
+		}))
+	b2 := buildBlock(t, b1, val, []*blockchain.Transaction{postTx})
+	mustAddBlock(t, c, b2)
+
+	likeTx := makeTx(blockchain.EventLikePost, bob.PubKeyHex(), "",
+		0, blockchain.MinFee, mustJSON(blockchain.LikePostPayload{PostID: "p1"}))
+	b3 := buildBlock(t, b2, val, []*blockchain.Transaction{likeTx})
+	mustAddBlock(t, c, b3)
+
+	n, _ := c.LikeCount("p1")
+	if n != 1 {
+		t.Errorf("LikeCount after like: got %d, want 1", n)
+	}
+	liked, _ := c.HasLiked("p1", bob.PubKeyHex())
+	if !liked {
+		t.Errorf("HasLiked after like: got false")
+	}
+
+	// Duplicate like — tx is skipped; counter stays at 1.
+	dupTx := makeTx(blockchain.EventLikePost, bob.PubKeyHex(), "",
+		0, blockchain.MinFee, mustJSON(blockchain.LikePostPayload{PostID: "p1"}))
+	b4 := buildBlock(t, b3, val, []*blockchain.Transaction{dupTx})
+	mustAddBlock(t, c, b4)
+	if n2, _ := c.LikeCount("p1"); n2 != 1 {
+		t.Errorf("LikeCount after duplicate: got %d, want 1 (tx should have been skipped)", n2)
+	}
+
+	unlikeTx := makeTx(blockchain.EventUnlikePost, bob.PubKeyHex(), "",
+		0, blockchain.MinFee, mustJSON(blockchain.UnlikePostPayload{PostID: "p1"}))
+	b5 := buildBlock(t, b4, val, []*blockchain.Transaction{unlikeTx})
+	mustAddBlock(t, c, b5)
+
+	n, _ = c.LikeCount("p1")
+	if n != 0 {
+		t.Errorf("LikeCount after unlike: got %d, want 0", n)
+	}
+}
+
+// TestFeedDeletePostByOther: only the author may delete their post.
+func TestFeedDeletePostByOther(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	alice := newIdentity(t)
+	mallory := newIdentity(t) // tries to delete alice's post
+	host := newIdentity(t)
+
+	genesis := addGenesis(t, c, val)
+	const postSize = uint64(100)
+	fee := blockchain.BasePostFee + postSize*blockchain.PostByteFee
+	fundAlice := makeTx(blockchain.EventTransfer, val.PubKeyHex(), alice.PubKeyHex(),
+		fee+5*blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	time.Sleep(2 * time.Millisecond)
+	fundMallory := makeTx(blockchain.EventTransfer, val.PubKeyHex(), mallory.PubKeyHex(),
+		5*blockchain.MinFee, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	b1 := buildBlock(t, genesis, val, []*blockchain.Transaction{fundAlice, fundMallory})
+	mustAddBlock(t, c, b1)
+
+	h := sha256.Sum256([]byte("body"))
+	postTx := makeTx(blockchain.EventCreatePost, alice.PubKeyHex(), "", 0, fee,
+		mustJSON(blockchain.CreatePostPayload{
+			PostID: "p1", ContentHash: h[:], Size: postSize, HostingRelay: host.PubKeyHex(),
+		}))
+	b2 := buildBlock(t, b1, val, []*blockchain.Transaction{postTx})
+	mustAddBlock(t, c, b2)
+
+	// Mallory tries to delete alice's post — block commits, tx is skipped.
+	delTx := makeTx(blockchain.EventDeletePost, mallory.PubKeyHex(), "", 0, blockchain.MinFee,
+		mustJSON(blockchain.DeletePostPayload{PostID: "p1"}))
+	b3 := buildBlock(t, b2, val, []*blockchain.Transaction{delTx})
+	mustAddBlock(t, c, b3)
+	rec, _ := c.Post("p1")
+	if rec == nil || rec.Deleted {
+		t.Fatalf("post was deleted by non-author: %+v", rec)
+	}
+}
+
+// silence unused-import lint if fmt ever gets trimmed from the feed tests.
+var _ = fmt.Sprintf

blockchain/types.go

@@ -11,8 +11,6 @@ type EventType string
 
 const (
 	EventRegisterKey    EventType = "REGISTER_KEY"
-	EventCreateChannel  EventType = "CREATE_CHANNEL"
-	EventAddMember      EventType = "ADD_MEMBER"
 	EventOpenPayChan    EventType = "OPEN_PAY_CHAN"
 	EventClosePayChan   EventType = "CLOSE_PAY_CHAN"
 	EventTransfer       EventType = "TRANSFER"
@@ -37,6 +35,17 @@ const (
 	EventMintNFT         EventType = "MINT_NFT"          // mint a new non-fungible token
 	EventTransferNFT     EventType = "TRANSFER_NFT"      // transfer NFT ownership
 	EventBurnNFT         EventType = "BURN_NFT"          // burn (destroy) an NFT
+
+	// ── Social feed (v2.0.0) ──────────────────────────────────────────────
+	// Replaces the old channel model with a VK/Twitter-style timeline.
+	// Posts are plaintext, publicly readable, size-priced. Bodies live in
+	// the relay feed-mailbox; on-chain we only keep metadata + author.
+	EventCreatePost      EventType = "CREATE_POST"       // author publishes a post
+	EventDeletePost      EventType = "DELETE_POST"       // author soft-deletes their post
+	EventFollow          EventType = "FOLLOW"            // follow another author's feed
+	EventUnfollow        EventType = "UNFOLLOW"          // unfollow an author
+	EventLikePost        EventType = "LIKE_POST"         // like a post
+	EventUnlikePost      EventType = "UNLIKE_POST"       // remove a previous like
 )
 
 // Token amounts are stored in micro-tokens (µT).
@@ -64,6 +73,31 @@ const (
 	// MinContactFee is the minimum amount a sender must pay the recipient when
 	// submitting an EventContactRequest (anti-spam; goes directly to recipient).
 	MinContactFee uint64 = 5_000 // 0.005 T
+
+	// ── Feed pricing (v2.0.0) ─────────────────────────────────────────────
+	// A post's on-chain fee is BasePostFee + bytes_on_disk × PostByteFee.
+	// The fee is paid by the author and credited in full to the hosting
+	// relay (the node that received POST /feed/publish and stored the body).
+	// Size-based pricing is what aligns incentives: a 200-byte tweet is
+	// cheap, a 256 KB video costs ~0.26 T — node operators' storage cost
+	// is covered.
+	//
+	// Note: BasePostFee is set to MinFee (1000 µT) because chain-level block
+	// validation requires every tx's Fee ≥ MinFee. So the true minimum a
+	// post can cost is MinFee + size × PostByteFee. A 0-byte post is
+	// rejected (Size must be > 0), so in practice a ~50-byte text post
+	// costs ~1050 µT (~$0.001 depending on token price).
+	BasePostFee    uint64 = 1_000 // 0.001 T flat per post — aligned with MinFee floor
+	PostByteFee    uint64 = 1     // 1 µT per byte of stored content
+
+	// MaxPostSize caps a single post's on-wire size (text + attachment, post
+	// compression). Hard limit — node refuses larger envelopes to protect
+	// storage and bandwidth.
+	MaxPostSize uint64 = 256 * 1024 // 256 KiB
+
+	// LikeFee / FollowFee / UnlikeFee / UnfollowFee / DeletePostFee all use
+	// MinFee (1000 µT) — standard tx fee paid to the validator. No extra
+	// cost; these events carry no body.
 )
 
 // Transaction is the atomic unit recorded in a block.
@@ -90,11 +124,66 @@ type RegisterKeyPayload struct {
 	X25519PubKey string `json:"x25519_pub_key,omitempty"` // hex Curve25519 key for E2E messaging
 }
 
-// CreateChannelPayload is embedded in EventCreateChannel transactions.
-type CreateChannelPayload struct {
-	ChannelID string `json:"channel_id"`
-	Title     string `json:"title"`
-	IsPublic  bool   `json:"is_public"`
+// ── Feed payloads (v2.0.0) ─────────────────────────────────────────────────
+
+// CreatePostPayload is embedded in EventCreatePost transactions. The body
+// itself is NOT stored on-chain — it lives in the relay feed-mailbox keyed
+// by PostID. On-chain we only keep author, size, hash, timestamp and any
+// reply/quote reference for ordering and proof of authorship.
+//
+// PostID is computed client-side as hex(sha256(author || content_hash || ts)[:16])
+// — same scheme as envelope IDs. Clients include it so the relay can store
+// the body under a stable key before the chain commit lands.
+//
+// HostingRelay is the node pubkey (Ed25519 hex) that accepted the POST
+// /feed/publish call and holds the body. Readers resolve it via the chain
+// and fetch the body directly from that relay (or via gossipsub replicas).
+// The fee is credited to this pub.
+//
+// QuoteOf / ReplyTo are mutually exclusive; set at most one. ReplyTo makes
+// the post a reply in a thread; QuoteOf creates a link/reference block.
+type CreatePostPayload struct {
+	PostID       string `json:"post_id"`
+	ContentHash  []byte `json:"content_hash"`            // sha256 of body-bytes, 32 B
+	Size         uint64 `json:"size"`                    // bytes on disk (compressed)
+	HostingRelay string `json:"hosting_relay"`           // hex Ed25519 of storing node
+	ReplyTo      string `json:"reply_to,omitempty"`      // parent post ID
+	QuoteOf      string `json:"quote_of,omitempty"`      // referenced post ID
+}
+
+// DeletePostPayload — author soft-deletes their own post. Stored marker
+// lets clients hide the post; relay can GC the body on the next sweep.
+type DeletePostPayload struct {
+	PostID string `json:"post_id"`
+}
+
+// FollowPayload / UnfollowPayload — follow graph. tx.From = follower,
+// tx.To = target. No body.
+type FollowPayload struct{}
+type UnfollowPayload struct{}
+
+// LikePostPayload / UnlikePostPayload — per-post like indicator. tx.From
+// = liker. The counter is derived on read.
+type LikePostPayload struct {
+	PostID string `json:"post_id"`
+}
+type UnlikePostPayload struct {
+	PostID string `json:"post_id"`
+}
+
+// PostRecord is what we store on-chain under post:<postID>. Consumers of
+// PostsByAuthor / query endpoints decode this.
+type PostRecord struct {
+	PostID       string `json:"post_id"`
+	Author       string `json:"author"`                  // hex Ed25519
+	ContentHash  []byte `json:"content_hash"`
+	Size         uint64 `json:"size"`
+	HostingRelay string `json:"hosting_relay"`
+	ReplyTo      string `json:"reply_to,omitempty"`
+	QuoteOf      string `json:"quote_of,omitempty"`
+	CreatedAt    int64  `json:"created_at"`              // unix seconds (tx timestamp)
+	Deleted      bool   `json:"deleted,omitempty"`
+	FeeUT        uint64 `json:"fee_ut"`                  // total fee paid
 }
 
 // RegisterRelayPayload is embedded in EventRegisterRelay transactions.
@@ -241,24 +330,6 @@ type BlockContactPayload struct {
 	Reason string `json:"reason,omitempty"`
 }
 
-// ChannelMember records a participant in a channel together with their
-// X25519 public key. The key is cached on-chain (written during ADD_MEMBER)
-// so channel senders don't have to fan out a separate /api/identity lookup
-// per recipient on every message — they GET /api/channels/:id/members
-// once and seal N envelopes in a loop.
-type ChannelMember struct {
-	PubKey       string `json:"pub_key"`        // Ed25519 hex
-	X25519PubKey string `json:"x25519_pub_key"` // optional; empty if member hasn't registered
-	Address      string `json:"address"`
-}
-
-// AddMemberPayload is embedded in EventAddMember transactions.
-// tx.From adds tx.To as a member of the specified channel.
-// If tx.To is empty, tx.From is added (self-join for public channels).
-type AddMemberPayload struct {
-	ChannelID string `json:"channel_id"`
-}
-
 // AddValidatorPayload is embedded in EventAddValidator transactions.
 // tx.From must already be a validator; tx.To is the new validator's pub key.
 //