Refactor documentation for splittable artifacts and update references

Updated various documentation files to clarify the handling of splittable artifacts, allowing for folder equivalents of key markdown files when they exceed size limits. Adjusted references in multiple sections to reflect this new structure, ensuring consistency across the research methodology. Enhanced clarity on the saving actions and artifact organization, particularly for `01_source_registry.md`, `02_fact_cards.md`, and `06_component_fit_matrix.md`. This change aims to improve usability and maintainability of the research documentation.

.cursor/skills/research/steps/03_engine-investigation.md

@@ -192,7 +192,7 @@ For every component/tool/library/service/pattern/algorithm that may be selected
 
 **API Capability Verification — Per-Mode (MANDATORY, BLOCKING for lead candidates)**:
 
-**Applicability**: this section applies only when the run is classified as **Technical-component selection** in the SKILL's Research Output Class section, and only to lead candidates that are libraries/SDKs/frameworks/services/protocols/data formats with multiple modes or configurations. For non-technical research (concept comparison, market/policy investigation, knowledge organization, root-cause analysis without tooling commitments), skip this entire sub-section and continue with the rest of Step 2 — the broader candidate implementation-limit search above is sufficient. State the skip explicitly once in `02_fact_cards.md`: `API Capability Verification: not applicable — this run is a Non-technical investigation, no library/SDK/service candidates`.
+**Applicability**: this section applies only when the run is classified as **Technical-component selection** in the SKILL's Research Output Class section, and only to lead candidates that are libraries/SDKs/frameworks/services/protocols/data formats with multiple modes or configurations. For non-technical research (concept comparison, market/policy investigation, knowledge organization, root-cause analysis without tooling commitments), skip this entire sub-section and continue with the rest of Step 2 — the broader candidate implementation-limit search above is sufficient. State the skip explicitly once in `02_fact_cards.md` (or in `02_fact_cards/00_summary.md` if split): `API Capability Verification: not applicable — this run is a Non-technical investigation, no library/SDK/service candidates`.
 
 Most libraries/SDKs/services expose **multiple modes or configurations** (e.g., monocular vs stereo VO, sync vs async API, batch vs streaming inference, write-through vs write-behind cache). Selecting a candidate "because it supports X" without pinning *which mode* the project will use, and *whether that exact mode produces the required outputs from the required inputs*, is the most common silent-failure path in research. A library can support a class of problem in mode A while being unusable for the project's specific configuration in mode B.
 
@@ -206,10 +206,10 @@ For every lead candidate that is a library/SDK/framework/service with multiple m
    2. *Project's exact mode*: "Show a minimum runnable example of `<library>` in `<the pinned mode>` with `<the project's input shape>`. What does it produce?"
    3. *Disqualifier probe*: "Does `<library>` `<the pinned mode>` produce `<the required output>`? Are there published limitations of `<the pinned mode>` for `<the project's runtime/hardware>`?"
 
-   For services without context7 coverage, use official docs site + WebFetch on the API reference page + the project's example/tutorial directory in the source repo. Append every consulted URL to `01_source_registry.md`.
+   For services without context7 coverage, use official docs site + WebFetch on the API reference page + the project's example/tutorial directory in the source repo. Append every consulted URL to `01_source_registry.md` (or the appropriate category file under `01_source_registry/` if split — see splittable-artifacts convention in `00_project-integration.md`).
 
 3. **Save a Minimum Viable Example (MVE) for the pinned mode.**
-   Append to `02_fact_cards.md` (or a sibling `02_mve_evidence.md`) at least one block per lead library candidate with:
+   Append to `02_fact_cards.md` / `02_fact_cards/` (or a sibling `02_mve_evidence.md`) at least one block per lead library candidate with:
 
    ```markdown
    ## MVE — <library> in <pinned mode>
@@ -225,7 +225,7 @@ For every lead candidate that is a library/SDK/framework/service with multiple m
    If no official example covers the project's exact configuration → the candidate cannot be marked `Selected` based on category fit alone. Status must be `Experimental only` (with required-evidence note) or `Rejected` (when the docs explicitly disqualify the configuration).
 
 4. **Bind every numbered Restriction and Acceptance Criterion to the candidate's pinned mode.**
-   For each numbered line in `restrictions.md` and `acceptance_criteria.md`, decide one of: `Pass` (the pinned mode satisfies it with cited evidence), `Fail` (the pinned mode contradicts it with cited evidence), `Verify` (no evidence either way; deeper investigation required), `N/A` (the line is irrelevant to this component area). Record this in `02_fact_cards.md` under the candidate's MVE block. The structural matrix in Step 7.5 reads from these bindings.
+   For each numbered line in `restrictions.md` and `acceptance_criteria.md`, decide one of: `Pass` (the pinned mode satisfies it with cited evidence), `Fail` (the pinned mode contradicts it with cited evidence), `Verify` (no evidence either way; deeper investigation required), `N/A` (the line is irrelevant to this component area). Record this in `02_fact_cards.md` (or the candidate's per-component file under `02_fact_cards/` if split) under the candidate's MVE block. The structural matrix in Step 7.5 reads from these bindings.
 
 5. **Treat "the same library in a different mode" as a different candidate.**
    If the project's pinned mode is `Monocular` but the only documented evidence covers `Stereo`, do not silently soften "rotation only" into "rotation + translation". Open a separate candidate row for the Monocular mode, with its own MVE, fit assessment, and disqualifiers. Two modes of one library are two distinct candidates for the purposes of this gate.
@@ -243,7 +243,7 @@ For every lead candidate that is a library/SDK/framework/service with multiple m
 **Search saturation rule**: Continue searching until new queries stop producing substantially new information. If the last 3 searches only repeat previously found facts, the sub-question is saturated.
 
 **Save action**:
-For each source consulted, **immediately** append to `01_source_registry.md` using the entry template from `references/source-tiering.md`.
+For each source consulted, **immediately** append to `01_source_registry.md` (or the appropriate category file under `01_source_registry/` if split) using the entry template from `references/source-tiering.md`.
 
 ---
 
@@ -273,7 +273,7 @@ Transform sources into **verifiable fact cards**:
   - ❓ Low: Inference or from unofficial sources
 
 **Save action**:
-For each extracted fact, **immediately** append to `02_fact_cards.md`:
+For each extracted fact, **immediately** append to `02_fact_cards.md` (or the appropriate category file under `02_fact_cards/` if split):
 ```markdown
 ## Fact #[number]
 - **Statement**: [specific fact description]
@@ -318,7 +318,7 @@ After initial fact extraction, review what you have found and identify **knowled
    - Failure cases and edge conditions
    - Recent developments that may change the picture
 
-4. **Update artifacts**: Append new sources to `01_source_registry.md`, new facts to `02_fact_cards.md`
+4. **Update artifacts**: Append new sources to `01_source_registry.md`, new facts to `02_fact_cards.md` (use the appropriate category files under `01_source_registry/` and `02_fact_cards/` if split)
 
 **Exit criteria**: Proceed to Step 4 when:
 - Every sub-question has at least 3 facts with at least one from L1/L2