bkpr: strings in structures should be const.

diff --git a/plugins/bkpr/account_entry.c b/plugins/bkpr/account_entry.c
index 0606c69b..a199fe42 100644
--- a/plugins/bkpr/account_entry.c
+++ b/plugins/bkpr/account_entry.c
@@ -16,7 +16,7 @@ const char *account_entry_tag_str(enum account_entry_tag tag)
 	return tags[tag];
 }
 
-bool account_entry_tag_find(char *str, enum account_entry_tag *tag)
+bool account_entry_tag_find(const char *str, enum account_entry_tag *tag)
 {
 	for (size_t i = 0; i < NUM_ACCOUNT_ENTRY_TAGS; i++) {
 		if (streq(str, tags[i])) {
diff --git a/plugins/bkpr/account_entry.h b/plugins/bkpr/account_entry.h
index 8823f672..ec6b8cca 100644
--- a/plugins/bkpr/account_entry.h
+++ b/plugins/bkpr/account_entry.h
@@ -14,5 +14,5 @@ enum account_entry_tag {
 const char *account_entry_tag_str(enum account_entry_tag tag);
 
 /* True if entry tag found, false otherwise */
-bool account_entry_tag_find(char *str, enum account_entry_tag *tag);
+bool account_entry_tag_find(const char *str, enum account_entry_tag *tag);
 #endif /* LIGHTNING_PLUGINS_BKPR_ACCOUNT_ENTRY_H */
diff --git a/plugins/bkpr/chain_event.h b/plugins/bkpr/chain_event.h
index e04ba6f4..d4ea73ef 100644
--- a/plugins/bkpr/chain_event.h
+++ b/plugins/bkpr/chain_event.h
@@ -19,10 +19,10 @@ struct chain_event {
 	u64 acct_db_id;
 
 	/* Name of the account this belongs to */
-	char *acct_name;
+	const char *acct_name;
 
 	/* Name of account this originated from */
-	char *origin_acct;
+	const char *origin_acct;
 
 	/* Tag describing the event */
 	const char *tag;
diff --git a/plugins/bkpr/channel_event.h b/plugins/bkpr/channel_event.h
index c844f82d..8b449b85 100644
--- a/plugins/bkpr/channel_event.h
+++ b/plugins/bkpr/channel_event.h
@@ -18,7 +18,7 @@ struct channel_event {
 	u64 acct_db_id;
 
 	/* Name of the account this belongs to */
-	char *acct_name;
+	const char *acct_name;
 
 	/* Tag describing the event */
 	const char *tag;
diff --git a/plugins/bkpr/channelsapy.h b/plugins/bkpr/channelsapy.h
index 1e4ccef2..d7c93884 100644
--- a/plugins/bkpr/channelsapy.h
+++ b/plugins/bkpr/channelsapy.h
@@ -5,7 +5,7 @@
 #include <ccan/tal/tal.h>
 
 struct channel_apy {
-	char *acct_name;
+	const char *acct_name;
 
 	struct amount_msat routed_in;
 	struct amount_msat routed_out;
diff --git a/plugins/bkpr/incomestmt.c b/plugins/bkpr/incomestmt.c
index 99908868..a73437e5 100644
--- a/plugins/bkpr/incomestmt.c
+++ b/plugins/bkpr/incomestmt.c
@@ -33,7 +33,7 @@ static struct account *get_account(struct account **accts,
 
 static struct income_event *chain_to_income(const tal_t *ctx,
 					    struct chain_event *ev,
-					    char *acct_to_attribute,
+					    const char *acct_to_attribute,
 					    struct amount_msat credit,
 					    struct amount_msat debit)
 {
@@ -98,7 +98,7 @@ static struct income_event *onchainfee_to_income(const tal_t *ctx,
  * by wrapping the desc in double-quotes ("). But what if
  * there's already double-quotes? Well we swap these to
  * single-quotes (') and then use the json_escape function */
-static char *csv_safe_str(const tal_t *ctx, char *input TAKES)
+static char *csv_safe_str(const tal_t *ctx, const char *input TAKES)
 {
 	struct json_escape *esc;
 	char *dupe;
diff --git a/plugins/bkpr/incomestmt.h b/plugins/bkpr/incomestmt.h
index b381598f..1857718c 100644
--- a/plugins/bkpr/incomestmt.h
+++ b/plugins/bkpr/incomestmt.h
@@ -6,9 +6,9 @@
 #include <stdio.h>
 
 struct income_event {
-	char *acct_name;
-	char *tag;
-	char *desc;
+	const char *acct_name;
+	const char *tag;
+	const char *desc;
 	struct amount_msat credit;
 	struct amount_msat debit;
 	/* Some CSVs require us to put fees on the
@@ -23,7 +23,7 @@ struct income_event {
 
 /* Each csv format has a header and a 'row print' function */
 struct csv_fmt {
-	char *fmt_name;
+	const char *fmt_name;
 	void (*emit_header)(FILE *);
 	void (*emit_entry)(const tal_t *, FILE *, struct income_event *);
 };
diff --git a/plugins/bkpr/onchain_fee.h b/plugins/bkpr/onchain_fee.h
index 03773a01..fde72cec 100644
--- a/plugins/bkpr/onchain_fee.h
+++ b/plugins/bkpr/onchain_fee.h
@@ -14,7 +14,7 @@ struct onchain_fee {
 	u64 acct_db_id;
 
 	/* Name of the account this belongs to */
-	char *acct_name;
+	const char *acct_name;
 
 	/* Transaction that we're recording fees for */
 	struct bitcoin_txid txid;
diff --git a/plugins/bkpr/recorder.h b/plugins/bkpr/recorder.h
index 1e508889..eef9e297 100644
--- a/plugins/bkpr/recorder.h
+++ b/plugins/bkpr/recorder.h
@@ -17,7 +17,7 @@ struct onchain_fee;
 
 struct fee_sum {
 	u64 acct_db_id;
-	char *acct_name;
+	const char *acct_name;
 	struct bitcoin_txid *txid;
 	struct amount_msat fees_paid;
 };
@@ -35,8 +35,8 @@ struct txo_set {
 struct rebalance {
 	u64 in_ev_id;
 	u64 out_ev_id;
-	char *in_acct_name;
-	char *out_acct_name;
+	const char *in_acct_name;
+	const char *out_acct_name;
 	struct amount_msat rebal_msat;
 	struct amount_msat fee_msat;
 };