docs: update sprint doc — mark state isolation fix complete

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sprint_2026_03.md

@@ -77,9 +77,13 @@ This sprint covers hardening, settings, and new capabilities before that happens
   - `ts_username` in SETTINGS_SCHEMA → pre-fills on load via `load_settings_on_startup`
   - `liveboard_name`, `default_use_case`, `default_llm` all pre-fill on startup
   - company no longer pre-filled (chat-driven) — working as intended
-- [~] **State Isolation Fix** ⚠️ PARTIAL — session logger fixed, prompt logger still broken
+- [x] **State Isolation Fix** ✅ — both loggers now fully per-session
   - Session logger: stored on `self._session_logger` (per controller instance) ✅
-  - Prompt logger: `reset_prompt_logger(session_id)` is called but `_prompt_logger` is still a module-level singleton — Session 2's reset overwrites Session 1's logger; **NOT fixed**
+  - Prompt logger: global singleton removed; `PromptLogger` instantiated directly per controller ✅
+    - `logged_completion()` and `log_researcher_call()` accept `logger=` param; if None, skips log
+    - `ThoughtSpotDeployer.prompt_logger` set from controller after construction
+    - `SmartDataAdjuster` accepts `prompt_logger=` constructor param
+    - Prompt log tab timer reads from `controller._prompt_logger` via `gr.State`
   - `inject_admin_settings_to_env()` still in use (deferred — requires cdw_connector refactor)
 
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