perf(agent): rombak alur AI agent — adaptif, hemat token, self-healing

Ganti explore phase MANDATORY (3 subagent tiap turn, boros) dengan
tool explore_codebase yang DIPUTUSKAN agent sendiri (lazy, token-aware):
- hapus ExploreService trait + with_explore + Phase 0 dari turn loop
- ExploreServiceImpl kini jadi tool 'explore_codebase' (1 context-scout
  subagent, read-only, cap output 4k chars)
- system prompt: instruksi TOKEN BUDGET (jawab langsung utk query simple,
  panggil explore_codebase sekali utk task kompleks)

Loop utama kini adaptif & self-healing:
- max_tokens adaptif (800/1600/4096 by request length) — bukan selalu 4096
- temperature 0.2 saat tool-calling, 0.7 utk final answer
- ErrorTracker: deteksi tool error berulang → inject recovery note,
  stop setelah 8 error total (bukan 50 iterasi sia-sia)
- auto-compact history > 60k chars sebelum LLM call
- tool output di-truncate ke 12k chars sebelum masuk konteks

Tambah 8 unit test (truncation, adaptive tokens, error tracker).

apps/domain/src/agent/prompt.rs

@@ -22,12 +22,20 @@ pub fn main_agent_prompt() -> String {
 You are Zesdex, an AI coding assistant. You have access to various tools \
 via native function calling to help the user.
 
+TOKEN BUDGET — BE EFFICIENT:
+- For simple/factual questions, answer directly. Do NOT call tools.
+- For complex or unfamiliar code tasks, call `explore_codebase` ONCE at the \
+start to locate relevant code, then work from that context.
+- Keep tool usage minimal: prefer `grep`/`glob`/`read` for targeted lookups; \
+avoid re-reading files you already have in context.
+- Keep responses concise; do not repeat tool output verbatim.
+
 CRITICAL DIRECTIVES & PRIORITY HIERARCHY:
 1. WORKFLOW FIRST: For any multi-step, complex, or non-trivial task, \
 you MUST prioritise using `workflow_run` (to construct and execute a \
 multi-phase YAML workflow) or `hive_mind` (to orchestrate parallel \
 autonomous agents). Workflows are your primary strategy.
-2. PLANNING & TODOS: Use `plan_enter` to establish high-level \
+2. PLANNING & TODOs: Use `plan_enter` to establish high-level \
 architectural plans and `todowrite` to maintain granular task checklists.
 3. REASONING: Use `seq_think` for deep step-by-step analysis.
 4. TOOL EXECUTION: Execute individual tools (file edits, terminal commands) \
@@ -70,6 +78,35 @@ executed, and modified files. Format as a clear bulleted list."
         .to_string()
 }
 
+// ---------------------------------------------------------------------------
+// Adaptive explore: directives
+// ---------------------------------------------------------------------------
+
+/// Directive for a single lightweight context-scout subagent.
+pub fn explore_scout_directive() -> String {
+    "\
+You are a codebase context scout. \
+Given the workspace root, quickly locate the code that is most relevant \
+to the user's request: \
+1. Run semantic_search once with the user's key terms. \
+2. Read up to the 3 most relevant files (use grep for symbols if needed). \
+3. Report a concise bullet list (max 15 bullets, under 1500 characters) of \
+what you found and exactly where (file paths). \
+Do NOT rebuild the index. Do NOT enumerate unrelated files. Be brief."
+        .to_string()
+}
+
+/// Build a system note injected after repeated tool errors to steer the
+/// agent toward an alternative approach instead of retrying the same call.
+pub fn error_recovery_note(tool_name: &str, last_error: &str) -> String {
+    format!(
+        "\
+[System note] The tool `{tool_name}` failed repeatedly with: \"{last_error}\". \
+Try an alternative approach (verify paths, correct arguments, use a \
+different tool, or finish without this tool). Do NOT retry the same call."
+    )
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -89,4 +126,18 @@ mod tests {
         assert!(prompt.contains("/home"));
         assert!(prompt.contains("/home/project"));
     }
+
+    #[test]
+    fn explore_scout_directive_is_concise_and_mentions_tools() {
+        let scout = explore_scout_directive();
+        assert!(scout.contains("scout"));
+        assert!(scout.contains("semantic_search"));
+    }
+
+    #[test]
+    fn error_recovery_note_suggests_alternative() {
+        let note = error_recovery_note("read", "File not found");
+        assert!(note.contains("read"));
+        assert!(note.contains("alternative"));
+    }
 }