Merge branch 'master' into merge/upstream-full

Resolve conflicts after master gained the flat-file database backend,
AI client, and other cproof-fork features:

- CHANGELOG: keep cproof-fork unreleased section atop full upstream
  history (0.17.0 / 0.16.0 / 0.15.1)
- src/command/cmd_ac.c: keep both upstream spellcheck AC and cproof
  /history switch|verify|export|import autocompletion
- src/config/preferences.c: merge upstream [spellcheck] group with the
  cproof [ai]/[ai/<provider>] groups
- src/database.c: take master (thin dispatcher); upstream SQLite
  improvements (v3 migration, auto_gchar) belong in database_sqlite.c
  and will land in a follow-up commit
- src/tools/autocomplete.c: take upstream unescape of search_str
- src/ui/statusbar.c: keep guint signatures (per project preference)
  and adapt _status_bar_draw_dbbackend to guint as well
- src/xmpp/jid.c: combine the new jid_is_valid/jid_is_valid_user_jid
  with the "(null)" legacy-placeholder guard in
  jid_create_from_bare_and_resource; use auto_gchar
- tests/functionaltests/proftest.c: keep unsigned-safe pre-check on
  output_len before subtracting OUTPUT_BUF_SIZE
- tests/unittests/unittests.c: keep upstream subdirectory include
  layout plus cproof-only test_ai_client/database_export/database_stress
- tests/unittests/test_jid.c: drop orphan top-level copy (the
  restructured version lives in tests/unittests/xmpp/test_jid.c)

Upstream is included up to 1ac05754b (release 0.18.0 era). Follow-up:
pull 1ac05754b..upstream/master (esp. 42a849d16 db migration fix and
4749645c7 receipt-request restore), and adapt the SQLite improvements
into database_sqlite.c.

src/command/cmd_defs.c

@@ -1269,8 +1269,8 @@ static const struct cmd_t command_defs[] = {
       CMD_TAGS(
               CMD_TAG_UI)
       CMD_SYN(
-              "/statusbar show name|number|read",
-              "/statusbar hide name|number|read",
+              "/statusbar show name|number|read|dbbackend",
+              "/statusbar hide name|number|read|dbbackend",
               "/statusbar maxtabs <value>",
               "/statusbar tablen <value>",
               "/statusbar tabmode default|dynamic|actlist",
@@ -1288,6 +1288,7 @@ static const struct cmd_t command_defs[] = {
               { "show|hide name", "Show or hide names in tabs." },
               { "show|hide number", "Show or hide numbers in tabs." },
               { "show|hide read", "Show or hide inactive tabs." },
+              { "show|hide dbbackend", "Show or hide the database backend indicator [sqlite] or [flatfile]." },
               { "self user|barejid|fulljid", "Show account user name, barejid, fulljid as status bar title." },
               { "self off", "Disable showing self as status bar title." },
               { "chat user|jid", "Show users name, or fulljid. Change needs a redraw/restart to take effect." },
@@ -1656,23 +1657,14 @@ static const struct cmd_t command_defs[] = {
     },
 
     { CMD_PREAMBLE("/logging",
-                   parse_args, 2, 3, &cons_logging_setting)
+                   parse_args, 0, 0, NULL)
       CMD_MAINFUNC(cmd_logging)
       CMD_TAGS(
               CMD_TAG_CHAT)
       CMD_SYN(
-              "/logging chat|group on|off")
+              "/logging")
       CMD_DESC(
-              "Configure chat logging. "
-              "Switch logging on or off. "
-              "Chat logging will be enabled if /history is set to on. "
-              "When disabling this option, /history will also be disabled. ")
-      CMD_ARGS(
-              { "chat on|off", "Enable/Disable regular chat logging." },
-              { "group on|off", "Enable/Disable groupchat (room) logging." })
-      CMD_EXAMPLES(
-              "/logging chat on",
-              "/logging group off")
+              "Deprecated. Use '/history' instead.")
     },
 
     { CMD_PREAMBLE("/states",
@@ -1872,18 +1864,34 @@ static const struct cmd_t command_defs[] = {
     },
 
     { CMD_PREAMBLE("/history",
-                   parse_args, 1, 1, &cons_history_setting)
+                   parse_args, 1, 2, &cons_history_setting)
       CMD_MAINFUNC(cmd_history)
       CMD_TAGS(
               CMD_TAG_UI,
               CMD_TAG_CHAT)
       CMD_SYN(
-              "/history on|off")
+              "/history on|off",
+              "/history backend",
+              "/history switch sqlite|flatfile",
+              "/history verify [<jid>]",
+              "/history export [<jid>]",
+              "/history import [<jid>]")
       CMD_DESC(
-              "Switch chat history on or off, /logging chat will automatically be enabled when this setting is on. "
-              "When history is enabled, previous messages are shown in chat windows.")
+              "Enable or disable chat history. "
+              "When on, messages are persisted via the active database backend and shown in chat windows. "
+              "When off, persistence stops and old history is hidden on chat-window open. "
+              "Use 'backend' to show the active database backend. "
+              "Use 'switch' to change the active database backend at runtime without reconnecting. "
+              "Use 'verify' to check integrity of stored message history. "
+              "Use 'export' to copy messages from SQLite to flat-file format, or 'import' to copy from flat-file to SQLite. "
+              "Both export and import merge with existing data (duplicates are skipped).")
       CMD_ARGS(
-              { "on|off", "Enable or disable showing chat history." })
+              { "on|off", "Enable or disable persistence and showing chat history." },
+              { "backend", "Show the name of the active database backend." },
+              { "switch sqlite|flatfile", "Switch the active database backend at runtime." },
+              { "verify [<jid>]", "Verify integrity of message history. Optionally specify a JID to check only one contact." },
+              { "export [<jid>]", "Export SQLite history to flat-file format. Optionally specify a JID to export only one contact." },
+              { "import [<jid>]", "Import flat-file history into SQLite. Optionally specify a JID to import only one contact." })
     },
 
     { CMD_PREAMBLE("/log",
@@ -2732,7 +2740,7 @@ static const struct cmd_t command_defs[] = {
               CMD_TAG_CHAT,
               CMD_TAG_DISCOVERY)
       CMD_SYN(
-              "/privacy logging on|redact|off",
+              "/privacy logging on|redact|off|flatfile",
               "/privacy os on|off")
       CMD_DESC(
               "Configure privacy settings. "
@@ -2740,12 +2748,13 @@ static const struct cmd_t command_defs[] = {
               "clientid to set the client identification name "
               "session_alarm to configure an alarm when more clients log in.")
       CMD_ARGS(
-              { "logging on|redact|off", "Switch chat logging. This will also disable logging in the internally used SQL database. Your messages will not be saved anywhere locally. This might have unintended consequences, such as not being able to decrypt OMEMO encrypted messages received later via MAM, and should be used with caution." },
+              { "logging on|redact|off|flatfile", "Switch chat logging backend. 'on' uses the SQLite database (default). 'flatfile' stores messages as plain-text files under ~/.local/share/profanity/flatlog/ that can be edited with any text editor. 'off' disables logging entirely. 'redact' keeps logging but replaces every message body with '[REDACTED]'. Note: 'off' may have side effects such as not being able to decrypt OMEMO messages received later via MAM. Backend changes ('on' / 'flatfile') take effect immediately when connected, otherwise on next connect." },
               { "os on|off", "Choose whether to include the OS name if a user asks for software information (XEP-0092)." }
               )
       CMD_EXAMPLES(
               "/privacy",
               "/privacy logging off",
+              "/privacy logging flatfile",
               "/privacy os off")
     },
 
@@ -2785,6 +2794,67 @@ static const struct cmd_t command_defs[] = {
               "/force-encryption policy block")
     },
 
+    { CMD_PREAMBLE("/ai",
+                   parse_args, 0, 5, NULL)
+      CMD_SUBFUNCS(
+              { "set", cmd_ai_set },
+              { "remove", cmd_ai_remove },
+              { "start", cmd_ai_start },
+              { "clear", cmd_ai_clear },
+              { "providers", cmd_ai_providers },
+              { "switch", cmd_ai_switch },
+              { "models", cmd_ai_models })
+      CMD_MAINFUNC(cmd_ai)
+      CMD_TAGS(
+              CMD_TAG_CHAT)
+      CMD_SYN(
+              "/ai",
+              "/ai set provider <name> <url>",
+              "/ai set token <provider> <token>",
+              "/ai set default-model <provider> <model>",
+              "/ai set custom <provider> <setting> <value>",
+              "/ai remove provider <name>",
+              "/ai providers",
+              "/ai start [<provider>] [<model>]",
+              "/ai switch <provider> [<model>]",
+              "/ai switch <model>",
+              "/ai models <provider>",
+              "/ai clear")
+      CMD_DESC(
+              "Interact with AI models via OpenAI-compatible APIs. "
+              "Supports multiple providers (openai, perplexity, custom). "
+              "Each provider has its own API key, endpoint, default model, and settings. "
+              "Chat history is maintained per session and not persisted locally.")
+      CMD_ARGS(
+              { "", "Display current AI settings and configured providers" },
+              { "set provider <name> <url>", "Add or update a provider with custom API endpoint" },
+              { "set token <provider> <token>", "Set API token for a provider (e.g., openai, perplexity)" },
+              { "set default-model <provider> <model>", "Set default model for a provider" },
+              { "set custom <provider> <setting> <value>", "Set provider-level setting (e.g., tools, search)" },
+              { "remove provider <name>", "Remove a custom provider" },
+              { "providers", "List configured providers with full details" },
+              { "start <provider> [<model>]", "Start new AI chat (space-separated, uses defaults if omitted)" },
+              { "switch <provider> [<model>]", "Switch to different provider (and optionally model)" },
+              { "models <provider>", "Fetch and display available models for provider" },
+              { "clear", "Clear current chat history" })
+      CMD_EXAMPLES(
+              "/ai",
+              "/ai set token openai sk-xxx",
+              "/ai set token perplexity pplx-xxx",
+              "/ai set provider custom https://my-api.com/v1/chat/completions",
+              "/ai set default-model perplexity sonar",
+              "/ai set custom perplexity tools enabled",
+              "/ai remove provider custom",
+              "/ai start",
+              "/ai start perplexity",
+              "/ai start perplexity sonar",
+              "/ai start openai gpt-4o",
+              "/ai switch gpt-4o",
+              "/ai switch openai gpt-5.4-nano",
+              "/ai models perplexity",
+              "/ai clear")
+    },
+
     // NEXT-COMMAND (search helper)
 };