diff --git a/openspec/changes/add-worker-original-filename-tracking/.openspec.yaml b/openspec/changes/add-worker-original-filename-tracking/.openspec.yaml
new file mode 100644
index 000000000..054b8c013
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+++ b/openspec/changes/add-worker-original-filename-tracking/.openspec.yaml
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-05-08
diff --git a/openspec/changes/add-worker-original-filename-tracking/proposal.md b/openspec/changes/add-worker-original-filename-tracking/proposal.md
new file mode 100644
index 000000000..1986c0d9c
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+++ b/openspec/changes/add-worker-original-filename-tracking/proposal.md
@@ -0,0 +1,41 @@
+## Why
+
+`_worker` 在收到 source artifact 時，會用 `SAFE_FILENAME_RE` 把非 ASCII 字元（中文、空格、括號、連字符）全部換成 `_`，再 `.strip("._")` 把開頭/結尾的底線清掉。對於常見的中文檔名 `許良宇圖書館建築_2026.ifc`，落地檔名變成 `54d77fe1_2026.ifc`（只剩 sha256 prefix + `2026.ifc`），原始檔名完全消失。
+
+更嚴重的是 `_worker` 寫入 source artifact `metadata.json` 時、寫入 `_index/source_artifacts.json` 時、以及 callback 給 `_bim-control` 的 conversion-result payload 中，**都不包含原檔名欄位**。也就是說：sanitize 之後再也找不回「這個 artifact 對應的原始 IFC 檔本來叫什麼」。
+
+`_bim-control` 在 `_update_artifacts_from_conversion` 中接收 callback 時，artifact 的 `name` 欄位寫死成「原始 IFC」/「已轉換 USDC」，不會反映實際檔名。
+
+實機驗證：13 個 89 MB 的中文檔名 IFC 副本（`許良宇圖書館建築_2026 - 複製 (N).ifc`）跑進 `_worker` 後，所有 disk 落地檔名都會變成形如 `<sha8>_<某個 ASCII 殘片>.ifc`，從 disk 與 `_bim-control` 都無法分辨哪個 artifact 對應原檔的第幾份副本。
+
+這次 change 在 metadata 層補上 `original_filename` 欄位，讓檔名 traceability 不會因為 sanitize 而斷裂；disk 檔名仍然 sanitize（保留 path 安全），但語意層保留原檔名。
+
+## What Changes
+
+- 在 `_worker` source artifact `metadata.json` 加入 `original_filename` 欄位，保留 `ArtifactIntakeRequest.filename` 的 raw 值（未 sanitize）。
+- 在 `_worker/data/objects/_index/source_artifacts.json` 每筆 entry 中也加入 `original_filename`，方便不開啟 metadata.json 也能查。
+- `POST /api/artifacts` response 多回 `original_filename`。
+- `POST /api/dev/ifc-sources/{source_id}/conversions` response 多回 `original_filename`（從 dev source 直接帶上原 `relative_path` 對應的檔名）。
+- `_worker` 完成轉檔後產出的 `result` payload（給 `GET /api/conversions/{id}/result`，以及 callback 給 `_bim-control`）多回 `original_filename`。
+- `_bim-control._update_artifacts_from_conversion` 收到 `original_filename` 時，將 source IFC artifact 的 `name` 欄位設為原檔名（沒帶就保留原本寫死的 fallback，向前相容）。
+- 既有 metadata.json / source_artifacts.json 沒有 `original_filename` 欄位的舊資料仍可正常讀取（讀取端用 `.get(...)` 容錯）。
+- 非目標：不改 disk 檔名 sanitize 邏輯、不改 `source_id` 計算公式、不改 path traversal 防護、不改 artifact ID schema、不做 disk 既有檔案的改名／移轉。
+
+## Capabilities
+
+### Modified Capabilities
+
+- `worker-artifact-pipeline`: 新增 Requirement「Worker preserves original filename in source metadata」，要求 source artifact metadata、`_index` 條目與 callback payload 都帶 `original_filename`。
+- `worker-dev-ifc-source-selection`: 修改 Requirement「Start Conversion From Selected Source」，把 selected-source conversion response 與後續 result／callback 都納入「必含 `original_filename`」的 scenario。
+
+### New Capabilities
+
+- 無。
+
+## Impact
+
+- `_worker`: 修改 [_worker/app/store.py](_worker/app/store.py) 的 `create_source_artifact` 與 `complete_conversion_job`：metadata dict 新增 `original_filename`、result payload 帶 `original_filename`、`_index/source_artifacts.json` 條目加欄位。修改 [_worker/app/main.py](_worker/app/main.py) 的兩個 conversion endpoint response 形狀。callback `_post_bim_control_result` 不需改（payload 已是 result dict）。新增 / 擴充 `_worker/tests/test_worker_api.py` 對應測試。
+- `_bim-control`: 修改 [_bim-control/app/main.py](_bim-control/app/main.py) `_update_artifacts_from_conversion`：當 result 包含 `original_filename` 時，設定 source IFC artifact 的 `name` 欄位為原檔名。新增 / 擴充 `_bim-control/tests/test_conversion_results_api.py` 對應測試。
+- `web-viewer-sample` / `bim-review-coordinator` / `bim-streaming-server`: 不需修改。`original_filename` 是 metadata 層的純加欄位，下游消費端可選擇是否使用。
+- 文件: `docs/contracts/worker-api.md`（如存在）需補上 `original_filename` 欄位說明。
+- 向前相容: 既有測試 fixture、archived spec、已落地的 `_worker/data/objects/...` 檔案結構不需改動。新欄位是 additive。
diff --git a/openspec/changes/add-worker-original-filename-tracking/specs/worker-artifact-pipeline/spec.md b/openspec/changes/add-worker-original-filename-tracking/specs/worker-artifact-pipeline/spec.md
new file mode 100644
index 000000000..016f5dd2f
--- /dev/null
+++ b/openspec/changes/add-worker-original-filename-tracking/specs/worker-artifact-pipeline/spec.md
@@ -0,0 +1,35 @@
+## ADDED Requirements
+
+### Requirement: Worker preserves original filename in source metadata
+
+`_worker` SHALL preserve the unsanitized client-provided filename as `original_filename` in source artifact metadata, the source artifact index, the source artifact API response, and the conversion result payload published to `_bim-control`. Disk object names MAY remain sanitized for path safety, but the metadata layer MUST keep the original filename so traceability survives across non-ASCII or special characters.
+
+#### Scenario: Source artifact metadata records the original filename
+
+- **WHEN** a client calls `POST /api/artifacts` with a `filename` containing non-ASCII characters or characters outside `[A-Za-z0-9_.-]`
+- **THEN** the source artifact `metadata.json` written under the versioned object layout MUST include `original_filename` equal to the request `filename` byte-for-byte (no sanitization), while the on-disk object key MAY use a sanitized filename for path safety
+
+#### Scenario: Source artifact index records the original filename
+
+- **WHEN** `_worker` upserts an entry into `data/objects/_index/source_artifacts.json`
+- **THEN** the entry MUST include `original_filename` so that consumers can recover the original filename without opening the per-artifact `metadata.json`
+
+#### Scenario: Source artifact API response includes the original filename
+
+- **WHEN** `POST /api/artifacts` succeeds
+- **THEN** the response body MUST include `original_filename` equal to the request `filename`
+
+#### Scenario: Conversion result includes the original filename
+
+- **WHEN** a conversion job started from any source artifact succeeds
+- **THEN** `GET /api/conversions/{conversion_job_id}/result` MUST include `original_filename` carried from the source artifact metadata
+
+#### Scenario: Callback to BIM control includes the original filename
+
+- **WHEN** `_worker` publishes a successful conversion result to `_bim-control` via the model-version conversion-result callback
+- **THEN** the callback payload MUST include `original_filename`, and `_bim-control` MUST set the source IFC artifact `name` field to that value when present, falling back to the existing default name when the field is absent
+
+#### Scenario: Backward-compatible reads of legacy metadata
+
+- **WHEN** `_worker` reads an existing `metadata.json` or `_index/source_artifacts.json` entry that was written before this requirement existed
+- **THEN** the read path MUST treat `original_filename` as optional and MUST NOT fail or refuse to serve the artifact when the field is missing
diff --git a/openspec/changes/add-worker-original-filename-tracking/specs/worker-dev-ifc-source-selection/spec.md b/openspec/changes/add-worker-original-filename-tracking/specs/worker-dev-ifc-source-selection/spec.md
new file mode 100644
index 000000000..69b205f88
--- /dev/null
+++ b/openspec/changes/add-worker-original-filename-tracking/specs/worker-dev-ifc-source-selection/spec.md
@@ -0,0 +1,25 @@
+## MODIFIED Requirements
+
+### Requirement: Start Conversion From Selected Source
+
+`_worker` SHALL provide `POST /api/dev/ifc-sources/{source_id}/conversions` to create a source artifact from a selected dev IFC and start a conversion job through the existing worker artifact pipeline. The response, the resulting source artifact metadata, and the conversion result MUST preserve the original dev IFC filename (including non-ASCII characters) as `original_filename`, even when the on-disk object name is sanitized for path safety.
+
+#### Scenario: Selected source starts worker job
+
+- **WHEN** a valid `source_id` is posted with tenant, project, model version, source system, and uploaded-by metadata
+- **THEN** `_worker` SHALL store the selected IFC in the versioned worker object layout, create a source artifact, create a conversion job, and return `source_artifact_id`, `artifact_group_id`, `conversion_job_id`, `status`, `original_filename`, and result lookup URLs
+
+#### Scenario: Conversion uses existing worker result contract
+
+- **WHEN** the selected-source conversion job succeeds
+- **THEN** `GET /api/conversions/{conversion_job_id}/result` SHALL return the same derived artifact, object URL, mapping URL, readiness, and lineage shape as conversions started from `POST /api/conversions`, plus `original_filename` carried from the source artifact metadata
+
+#### Scenario: Unknown source is rejected
+
+- **WHEN** `POST /api/dev/ifc-sources/{source_id}/conversions` is called with an unknown, stale, non-IFC, or out-of-root `source_id`
+- **THEN** `_worker` MUST return a 4xx response and MUST NOT create a source artifact or conversion job
+
+#### Scenario: Non-ASCII source filename is preserved end-to-end
+
+- **WHEN** a dev IFC under `WORKER_DEV_STORAGE_ROOT` has a filename containing non-ASCII characters (for example, traditional Chinese characters, spaces, or parentheses)
+- **THEN** the selected-source conversion response, the worker source `metadata.json`, the conversion result, and the `_bim-control` callback payload MUST all include `original_filename` equal to the original `relative_path` filename, even though the on-disk object key uses a sanitized form for path safety
diff --git a/openspec/changes/add-worker-original-filename-tracking/tasks.md b/openspec/changes/add-worker-original-filename-tracking/tasks.md
new file mode 100644
index 000000000..4fe46da4e
--- /dev/null
+++ b/openspec/changes/add-worker-original-filename-tracking/tasks.md
@@ -0,0 +1,54 @@
+## 1. Preparation And Impact Review
+
+- [ ] 1.1 Re-read `_worker/app/store.py`、`_worker/app/main.py`、`_worker/app/models.py`、`_bim-control/app/main.py` 中跟 source artifact metadata、conversion result、callback 有關的程式碼，確認加欄位的最小改動面。
+- [ ] 1.2 Run GitNexus impact analysis for `create_source_artifact`、`complete_conversion_job`、`_post_bim_control_result`、`_update_artifacts_from_conversion`；確認 HIGH/CRITICAL 風險前回報。
+- [ ] 1.3 列出既有 `_worker/data/objects/_index/source_artifacts.json`、metadata.json fixture 是否含舊資料；確認向前相容讀取策略（`.get("original_filename", None)`）。
+- [ ] 1.4 確認 `ArtifactIntakeRequest.filename` 欄位本身已是 raw（未 sanitize），可以直接保存到 metadata 不需重做 decode。
+
+## 2. Spec Deltas
+
+- [ ] 2.1 在 `openspec/changes/add-worker-original-filename-tracking/specs/worker-artifact-pipeline/spec.md` 新增 Requirement「Worker preserves original filename in source metadata」與其 scenarios。
+- [ ] 2.2 在 `openspec/changes/add-worker-original-filename-tracking/specs/worker-dev-ifc-source-selection/spec.md` 修改 Requirement「Start Conversion From Selected Source」，確保 response shape 必含 `original_filename`。
+- [ ] 2.3 Run `openspec validate add-worker-original-filename-tracking`。
+
+## 3. `_worker` Source Artifact Metadata
+
+- [ ] 3.1 修改 `_worker/app/store.py` `create_source_artifact()` 的 metadata dict，加入 `original_filename: str = request.filename`（保留 raw，不經 `safe_filename`）。
+- [ ] 3.2 修改 `_worker/app/store.py` `_upsert_source_index()` 寫入 `_index/source_artifacts.json` 的 entry，加入 `original_filename`。
+- [ ] 3.3 修改 `_worker/app/store.py` `create_source_artifact()` 的 return dict，加入 `original_filename`。
+- [ ] 3.4 確認 `_worker/app/store.py` `complete_conversion_job()` 從 `source["metadata"]` 取得 `original_filename` 並寫進 result payload（給 callback 與 GET result 用）。
+
+## 4. `_worker` API Response Shape
+
+- [ ] 4.1 修改 `_worker/app/main.py` `POST /api/artifacts` 的 response，確認 `original_filename` 在 response body（透過 `create_source_artifact` 的 return dict 自動帶出）。
+- [ ] 4.2 修改 `_worker/app/main.py` `POST /api/dev/ifc-sources/{source_id}/conversions` 的 response，加入 `original_filename`（從 `source_item["filename"]` 取，這是原 `relative_path` 對應的純檔名）。
+- [ ] 4.3 修改 `_worker/app/main.py` `GET /api/conversions/{id}/result` 透過 `complete_conversion_job` 自然帶出 `original_filename`，無需個別處理。
+
+## 5. `_bim-control` Artifact Name Mapping
+
+- [ ] 5.1 修改 `_bim-control/app/main.py` `_update_artifacts_from_conversion()`：source IFC artifact upsert 時，`name` 欄位優先用 `result.get("original_filename")`，fallback 保留現有「原始 IFC」字串。
+- [ ] 5.2 USDC artifact 的 `name` 欄位保持現有「已轉換 USDC」（USDC 是 worker 自己生的衍生檔，不需要展示原檔名）。
+- [ ] 5.3 確認 `_bim-control` 沒有任何 schema validation 會擋掉 result payload 多帶的欄位（目前是 `dict[str, Any]` 接收，OK）。
+
+## 6. Tests
+
+- [ ] 6.1 `_worker/tests/test_worker_api.py` 新增測試：上傳含中文檔名的 IFC，確認 metadata.json、`_index/source_artifacts.json`、API response 都含 `original_filename` 等於原檔名；disk filename 仍 sanitize。
+- [ ] 6.2 `_worker/tests/test_worker_api.py` 新增測試：selected-source conversion (dev IFC) 完成後，`GET /api/conversions/{id}/result` 包含 `original_filename`。
+- [ ] 6.3 `_worker/tests/test_worker_store.py` 補測 `create_source_artifact` 直接呼叫時 metadata 含 `original_filename`。
+- [ ] 6.4 `_bim-control/tests/test_conversion_results_api.py` 新增測試：POST conversion-result 含 `original_filename` 時，artifacts.json 的 source IFC entry `name` 欄位 = 原檔名；不含 `original_filename` 時 fallback 保持原行為。
+- [ ] 6.5 確認既有測試（無 `original_filename` 的舊 fixture）仍綠燈，驗證向前相容。
+
+## 7. Documentation
+
+- [ ] 7.1 若 `docs/contracts/worker-api.md` 存在，補上 `original_filename` 欄位說明（位置：source artifact response、conversion result、callback payload）。
+- [ ] 7.2 `_worker/README.md` API 段落如有列 response 範例，補欄位（可選，不阻擋）。
+- [ ] 7.3 `_bim-control/README.md` 不需改（callback 接收端形狀不變，只是多接受一個欄位）。
+
+## 8. Validation And Review
+
+- [ ] 8.1 `cd _worker && python -m pytest tests -q` 全綠。
+- [ ] 8.2 `cd _bim-control && python -m pytest tests -q` 全綠。
+- [ ] 8.3 Run `openspec validate add-worker-original-filename-tracking` 通過。
+- [ ] 8.4 GitNexus detect_changes 確認 affected scope 只在 `_worker` 與 `_bim-control` 範圍內。
+- [ ] 8.5 PR 描述列出向前相容性說明（既有資料 / 既有 callback 沒帶 `original_filename` 仍能運作）。
+- [ ] 8.6 Smoke：手動跑一次中文檔名 IFC 從 storage 進 worker、callback 到 `_bim-control` 的完整流程，確認 `_bim-control` artifact `name` 顯示原檔名。