# Iteration 06 Report - Error Handling and Fault Isolation

Date: 2026-03-01T09:01:57Z
Branch: codex/review/i06
Focus: Iteration 6 - error handling and fault isolation

## Mission Rewritten as Concise EARS Requirements
1. When iteration state indicates `current_iteration=6`, the run shall prioritize error handling and fault-isolation transparency.
2. If iteration 5 lessons emphasize explicit integrity contracts across read/write boundaries, iteration 6 shall carry that lesson by applying explicit integrity metadata across source-preparation and synthesis boundaries.
3. When a document source fails during download or upload preparation, the system shall record structured failure metadata with source and phase context.
4. If at least one document is prepared successfully, the final report shall include preparation-failure metadata and shall not silently discard skipped sources.
5. If no documents are prepared, the tool shall return structured `make_tool_error()` output and stop before synthesis.
6. The run shall persist findings by severity, exploit reasoning, concrete fixes, validation evidence, lessons learned, and next-iteration hypotheses.

## Scope Detection Evidence (Before/After Git Transitions)
- Before transitioning from detached `HEAD` to review branch:
  - `{"mode": "none", "reason": "No local changes and no ahead commits to review.", "branch": "HEAD", "base_branch": "main", "uncommitted_files": 0, "ahead_commits": 0, "pr_context": false, "pr_url": null}`
- After creating `codex/review/i06` from `codex/review-mainline`:
  - `{"mode": "commits", "reason": "Branch is ahead of base with no local unstaged/uncommitted files.", "branch": "codex/review/i06", "base_branch": "main", "uncommitted_files": 0, "ahead_commits": 10, "pr_context": false, "pr_url": null}`

## Required Reading Checklist
- `AGENTS.md`, `src/AGENTS.md`, `tests/AGENTS.md`
- `docs/ARCHITECTURE.md`, `docs/DIAGRAMS.md`
- `docs/tutorials/ADDING_A_TOOL.md`, `docs/tutorials/WRITING_TESTS.md`

## Findings (Ordered by Severity)

### F-601 (Medium) - Partial source failures were silently omitted from `research_document` responses
- Evidence:
  - `src/video_research_mcp/tools/research_document_file.py:123` and `:152` logged failures and continued.
  - `src/video_research_mcp/tools/research_document.py:77` consumed prepared sources but previously had no response field for skipped-source diagnostics.
- Exploit reasoning:
  - Callers could treat synthesis output as complete source coverage when one or more sources were skipped, reducing trust and potentially causing decisions based on incomplete evidence.
- Concrete fix:
  - Added `_prepare_all_documents_with_issues(...)` to capture per-source preparation failures and propagated `preparation_issues` into `DocumentResearchReport` output.
- Implementation status:
  - Implemented with targeted regression coverage.

### F-602 (Low) - Preparation failure metadata lacked explicit schema contract
- Evidence:
  - Prior `DocumentResearchReport` schema had no preparation-diagnostics field.
- Exploit reasoning:
  - Missing contract-level field made partial-failure disclosure inconsistent and harder to validate/test across clients.
- Concrete fix:
  - Added `DocumentPreparationIssue` model and `preparation_issues` list field to `DocumentResearchReport`.
- Implementation status:
  - Implemented with tool-level response assertion test.

## Implemented Changes
- `src/video_research_mcp/tools/research_document_file.py`
  - Added `_prepare_all_documents_with_issues(...)` to collect download/upload issue metadata.
  - Kept `_prepare_all_documents(...)` as a backward-compatible wrapper.
- `src/video_research_mcp/tools/research_document.py`
  - Switched to issue-aware preparation helper and propagated issues through quick/full synthesis paths.
- `src/video_research_mcp/models/research_document.py`
  - Added `DocumentPreparationIssue` model and `preparation_issues` field on `DocumentResearchReport`.
- `tests/test_research_document_tools.py`
  - Updated preparation mocks to issue-aware helper.
  - Added `test_surfaces_preparation_issues` regression.
- `tests/test_research_document_file.py`
  - Added helper-level regression for mixed success/failure source preparation.

## Validation Evidence
- Lint:
  - `uv run ruff check src/video_research_mcp/models/research_document.py src/video_research_mcp/tools/research_document.py src/video_research_mcp/tools/research_document_file.py tests/test_research_document_tools.py tests/test_research_document_file.py`
- Tests:
  - `PYTHONPATH=src uv run pytest tests/test_research_document_tools.py tests/test_research_document_file.py -v`
  - Result: 23 passed

## Reflective Self-Learning Loop
- Observe evidence:
  - Source-preparation failures were logged but not included in structured output.
- Infer root causes:
  - Availability-oriented continuation logic lacked an explicit outward-facing fault contract.
- Proposed fix strategies:
  - Introduce structured preparation issue capture at the helper boundary.
  - Add schema field for preparation issues and enforce propagation in all synthesis paths.
- Validate fixes:
  - Added helper/tool regression tests covering mixed success/failure scenarios; targeted lint/tests pass.
- Confidence change:
  - Fault-isolation transparency confidence: 0.60 -> 0.87.
  - Response-contract clarity confidence: 0.63 -> 0.86.
  - Overall iteration-6 objective confidence: 0.61 -> 0.87.

## Lesson-Carried Remediation (Required N-1 linkage)
- Derived from iteration 5 lesson: integrity controls must treat read/write paths as one explicit contract.
- Applied in iteration 6:
  - Added explicit integrity metadata (`preparation_issues`) spanning both preparation-write decisions (download/upload success/failure) and synthesis-read consumers.

## Lessons Learned
1. Fault isolation without explicit response-level diagnostics creates silent degradation risk.
2. Backward-compatible wrappers help introduce stronger contracts without destabilizing existing call sites.
3. Response schema updates plus regression tests are required to keep fault metadata durable across refactors.

## Next-Iteration Hypotheses (Iteration 7)
1. Build adversarial tests for prompt-injection strings in content/document inputs to validate tool misuse resistance.
2. Verify that untrusted content cannot alter system/tool instructions used by Gemini prompts.
3. Add detection guidance for high-risk tool composition patterns where untrusted text is concatenated with privileged instructions.
