fix(reliability): llm-retry — empty response detection, configurable max_tokens, connector timeout

Issue #5: detect empty string from llm_extract_text() as an error in handle_chat,
handle_chat_as_soul, and handle_dharma_room_turn. The C runtime silently returns ""
when the LLM response content array is missing or all blocks fail to parse; without
this guard the empty string passes through to callers as a silent empty reply.

Issue #9: make agentic_loop max_tokens configurable via NEURON_LLM_MAX_TOKENS env
var (default 4096). The hardcoded value is marginal for long tool chains (8 iterations
x 4096 tokens); operators can now set 8192+ for complex multi-step tasks without
rebuilding. Non-agentic path (llm_call_system) still uses the C runtime hardcode —
that fix lives in el_runtime.c (see TODO block added in this commit).

Issue #10: increase connector_tools_json and tool_auto_approved curl --max-time from
2s to 5s to reduce false-empty tool lists when neuron-connectd is under transient
load. Graceful degradation to [] on bridge down is unchanged.

Issues #1/#2/#3/#4/#6/#8: documented as TODO comments in chat.el. These require
targeted C runtime changes in el_runtime.c (llm_provider_request retry loop,
EL_LLM_TIMEOUT_MS separation, HTTP 429 backoff, 5xx retry, EL_HTTP_MAX_RESPONSE_BYTES
cap). Architectural decisions recorded so they are traceable to root causes.

chat.el

@@ -380,9 +380,13 @@ fn handle_chat(body: String) -> String {
 
     let raw_response: String = llm_call_system(model, full_system, message)
 
+    // Issue #5: also catch empty string — llm_extract_text() in el_runtime.c silently
+    // returns "" when the response content array is missing or all blocks fail to parse.
+    // Without this guard an empty reply passes through as a silent empty response.
     let is_error: Bool = str_starts_with(raw_response, "{\"error\"")
         || str_starts_with(raw_response, "{\"type\":\"error\"")
         || str_contains(raw_response, "authentication_error")
+        || str_eq(raw_response, "")
     if is_error {
         return "{\"error\":\"llm unavailable\",\"response\":\"\"}"
     }
@@ -447,6 +451,42 @@ fn studio_tools_json() -> String {
     "]"
 }
 
+// ---------------------------------------------------------------------------
+// LLM reliability — issues that require C runtime fixes (el_runtime.c).
+// These cannot be addressed at the EL layer; they are documented here so the
+// symptoms are traceable back to their root causes.
+//
+// Issue #1 (no retry on timeout/connection error):
+//   http_do() in el_runtime.c calls curl_easy_perform() once. On
+//   CURLE_OPERATION_TIMEDOUT / CURLE_COULDNT_CONNECT / CURLE_RECV_ERROR it
+//   returns http_error_json() with no retry. Fix: add a retry loop (max 3
+//   attempts, exponential back-off starting at 1s) inside llm_provider_request().
+//
+// Issue #2 (60s timeout applies to all HTTP calls including LLM):
+//   EL_HTTP_TIMEOUT_MS defaults to 60000ms for every http_do() call.
+//   Fix: introduce EL_LLM_TIMEOUT_MS (default 120000) used only by
+//   llm_provider_request(); leave EL_HTTP_TIMEOUT_MS (default 30000) for
+//   general service calls to avoid holding connections for 60s.
+//
+// Issue #3 (HTTP 429 causes silent provider failover, not backoff):
+//   llm_chain_call() advances to the next provider on any JSON-prefixed response
+//   including 429. Fix: parse HTTP status via curl_easy_getinfo; on 429 sleep
+//   Retry-After seconds (default 5s) then retry the same provider up to 3 times.
+//
+// Issue #4 (HTTP 500/502 crashes the request silently):
+//   Same path as #3 — 5xx responses cause immediate provider failover with no
+//   retry. Fix: retry with exponential back-off (1s, 2s, 4s) before advancing.
+//
+// Issue #6 (no secondary LLM fallback in production):
+//   Set NEURON_LLM_1_URL/KEY/FORMAT in ExternalSecret to a secondary provider
+//   (e.g. Gemini). No C code change required; llm_chain_call() already iterates.
+//
+// Issue #8 (LLM response size unbounded — memory-only cap):
+//   HttpBuf grows via realloc() with no hard limit. Fix: add
+//   EL_HTTP_MAX_RESPONSE_BYTES (default 10MiB) cap in httpbuf_append() and
+//   return http_error_json("response too large") on overflow.
+// ---------------------------------------------------------------------------
+
 fn agentic_api_key() -> String {
     let k1: String = env("ANTHROPIC_API_KEY")
     if !str_eq(k1, "") {
@@ -498,7 +538,7 @@ fn agentic_tools_with_web() -> String {
 // Short timeout + empty-array fallback: if the bridge is down, the soul runs
 // exactly as before with only its built-in tools (graceful degradation).
 fn connector_tools_json() -> String {
-    let raw: String = exec_capture("curl -s --max-time 2 http://127.0.0.1:7771/mcp/tools")
+    let raw: String = exec_capture("curl -s --max-time 5 http://127.0.0.1:7771/mcp/tools")
     if str_eq(raw, "") {
         return "[]"
     }
@@ -543,7 +583,7 @@ fn tool_auto_approved(tool_name: String) -> Bool {
     if !str_starts_with(tool_name, "mcp__") {
         return false
     }
-    let raw: String = exec_capture("curl -s --max-time 2 http://127.0.0.1:7771/mcp/auto-approved")
+    let raw: String = exec_capture("curl -s --max-time 5 http://127.0.0.1:7771/mcp/auto-approved")
     if str_eq(raw, "") {
         return false
     }
@@ -913,6 +953,14 @@ fn agentic_loop(session_id: String, model: String, safe_sys: String, tools_json:
     let iteration: Int = 0
     let keep_going: Bool = true
 
+    // Issue #9: agentic max_tokens configurable via NEURON_LLM_MAX_TOKENS env var.
+    // Default 4096 is marginal for long tool chains (8 iterations x 4096 tokens).
+    // Set to 8192+ for complex multi-step tasks.
+    // Note: llm_provider_request() in el_runtime.c also hardcodes 4096 for the
+    // llm_call_system() (non-agentic) path; that requires a C runtime change.
+    let max_tokens_env: String = env("NEURON_LLM_MAX_TOKENS")
+    let max_tokens_str: String = if str_eq(max_tokens_env, "") { "4096" } else { max_tokens_env }
+
     // Suspension state — captured at top level so it escapes the while body.
     let pending: Bool = false
     let pend_tool_id: String = ""
@@ -921,7 +969,7 @@ fn agentic_loop(session_id: String, model: String, safe_sys: String, tools_json:
 
     while keep_going && iteration < 8 {
         let req_body: String = "{\"model\":\"" + model + "\""
-            + ",\"max_tokens\":4096"
+            + ",\"max_tokens\":" + max_tokens_str
             + ",\"system\":\"" + safe_sys + "\""
             + ",\"tools\":" + tools_json
             + ",\"messages\":" + messages
@@ -1201,9 +1249,11 @@ fn handle_chat_as_soul(body: String) -> String {
 
     let raw_response: String = llm_call_system(model, system_prompt, eff_message)
 
+    // Issue #5: empty string catch — same rationale as handle_chat.
     let is_error: Bool = str_starts_with(raw_response, "{\"error\"")
         || str_starts_with(raw_response, "{\"type\":\"error\"")
         || str_contains(raw_response, "authentication_error")
+        || str_eq(raw_response, "")
     if is_error {
         return "{\"error\":\"llm unavailable\",\"response\":\"\",\"speaker_slug\":\"" + speaker + "\",\"model\":\"" + model + "\"}"
     }
@@ -1250,9 +1300,11 @@ fn handle_dharma_room_turn(body: String) -> String {
 
     let raw_response: String = llm_call_system(model, system_prompt, transcript)
 
+    // Issue #5: empty string catch — same rationale as handle_chat.
     let is_error: Bool = str_starts_with(raw_response, "{\"error\"")
         || str_starts_with(raw_response, "{\"type\":\"error\"")
         || str_contains(raw_response, "authentication_error")
+        || str_eq(raw_response, "")
     if is_error {
         return "{\"error\":\"llm unavailable\",\"response\":\"\",\"cgi_id\":\"" + cgi_id + "\"}"
     }