docs: introduce standard AI log entry format

- add standardized AI BUILD ENTRY and AI PLAN ENTRY format
- improve consistency of AI development logs
- update instructions-agent.md

instructions-agent.md

@@ -116,6 +116,11 @@ Each worklog entry must include:
 - result
 - unresolved issues, if any
 
+Validation logging rule:
+- If validation commands such as `make fix`, `make quality`, `pytest`, or other checks are executed during the task, the worklog entry must record them explicitly.
+- The value `validation: not run` may only be used if no validation commands were executed.
+- The worklog entry must reflect the actual commands run during the task.
+
 Each prompt log entry must include:
 - date
 - task type (`plan` or `build`)
@@ -128,3 +133,57 @@ Rules:
 - Store only concise user-facing summaries.
 - Keep entries chronological.
 - Even small but meaningful tasks must be logged.
+
+## Standard AI Log Entry Format
+
+To ensure consistency and readability of long AI-assisted development histories, all log entries must follow a standardized block format.
+
+Agents must write log entries using the following structure.
+
+Example for build tasks:
+
+### AI BUILD ENTRY
+Date: YYYY-MM-DD  
+Task: build  
+Objective: short description of the task
+
+Files Modified:
+- file/path/example.py
+- another/file.md
+
+Key Decisions:
+- short bullet explaining important choices
+
+Validation:
+- make fix (passed)
+- make quality (passed)
+
+Result:
+- short description of what changed or was achieved
+
+Open Issues:
+- optional list of unresolved problems
+
+Example for plan tasks:
+
+### AI PLAN ENTRY
+Date: YYYY-MM-DD  
+Task: plan  
+Objective: short description of planning objective
+
+Files Inspected:
+- src/app/example.py
+- specs/example_spec.md
+
+Proposed Changes:
+- summary of planned changes
+
+Notes:
+- optional relevant observations
+
+Rules:
+- Always use these headers exactly (`AI BUILD ENTRY` or `AI PLAN ENTRY`).
+- Keep entries concise and structured.
+- Do not include chain-of-thought reasoning.
+- Use bullet points when possible.
+- This format must be used when updating `docs/ai-worklog.md`.