mod_callcenter: Add agent-originate-check pre-originate hook

[shaunjstokes]

Closes #2989

Summary

• Add optional per-agent agent-originate-check attribute that executes a FreeSWITCH API command before originating
• If the command returns "false", originate is skipped — no SIP INVITE, no call leg
• Fail-open: any other return value (including errors) proceeds normally
• Fully backward-compatible — no behaviour change when the attribute is unset

Changes

src/mod/applications/mod_callcenter/mod_callcenter.c:

• Add agent_originate_check VARCHAR(1024) to agents table schema
• Add reactive migration via switch_cache_db_test_reactive() for existing databases
• Add agent_originate_check field to cc_agent_update() for runtime agent set commands
• Load agent-originate-check XML attribute in load_agent()
• Add agent_originate_check to all three SQL SELECT queries (position argv[19])
• Add pre-originate check block using switch_api_execute() before switch_ivr_originate()
• Add SUBSCRIBER_ABSENT cause handling with configurable delay (no_answer_delay_time, 5s floor)
• Update help syntax and console autocomplete

How It Works

1. mod_callcenter selects an agent and checks if agent_originate_check is set
2. If set, the value is split on the first space into api_cmd and api_args
3. The command is executed via switch_api_execute(api_cmd, api_args, NULL, &stream)
4. If stream.data equals "false" (case-insensitive), a skip_originate flag is set
5. When skipped, cause is set to SUBSCRIBER_ABSENT and the normal failure path runs (setting delay_next_agent_call)
6. When not skipped, switch_ivr_originate() proceeds as normal

Design Decisions

• Generic API execution — not tied to any specific language or backend. Works with lua, curl, python, or any registered FreeSWITCH API command
• Fail-open — errors, empty responses, or missing attributes all result in normal origination. No risk of silently breaking existing setups
• No goto done — the skip flows through the existing failure handling block so delay_next_agent_call is set correctly, preventing tight agent loops
• Local skip_originate flag — avoids altering the existing status variable which is initialised to SWITCH_STATUS_FALSE
• Configurable delay — uses the agent's existing no_answer_delay_time with a 5-second minimum floor to prevent rapid cycling

Testing

• Configured agent-originate-check with a Lua script that queries a SIP registrar database
• Verified registered agents receive calls normally
• Verified unregistered agents are skipped with no SIP INVITE and no CDR
• Verified skipped agents receive a delay before being retried
• Verified the feature is inactive when the attribute is empty or unset
• Verified fail-open behaviour when the API command errors

Example Usage

XML config:

<agent name="1001@example.com"
       agent-originate-check="lua agent_handler.lua 1001 example.com" />

Runtime via fs_cli:

callcenter_config agent set agent_originate_check 1001@example.com lua agent_handler.lua 1001 example.com