chore: add send file sandbox evidence package

docs/source-discovery/2026-07-10-send-file-sandbox-gate.md

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+# 2026-07-10 R9 Send-file sandbox evidence gate
+
+## Decision
+
+Local development still cannot log in to iSphere/IMPlatformClient, so real file upload must not be enabled from local-only evidence.
+
+R9 prepares a one-pass online/internal sandbox package for collecting the missing evidence. The package is intentionally operator-driven:
+
+- it does not click, type, upload, hook, inject, or send automatically;
+- the operator manually sends exactly one approved sandbox file;
+- before/after read-only recorder output and completed operator fields are returned for validation;
+- production `isphere_send_file` remains blocked until the returned package passes validation.
+
+## Package
+
+Builder:
+
+```powershell
+powershell -NoProfile -ExecutionPolicy Bypass -File scripts\package-send-file-sandbox-gate.ps1
+```
+
+Verifier:
+
+```powershell
+powershell -NoProfile -ExecutionPolicy Bypass -File scripts\verify-send-file-sandbox-gate-package.ps1
+```
+
+Expected generated zip:
+
+```text
+runs\send-file-sandbox-gate-package.zip
+```
+
+## Returned-package validator
+
+Use this after an online/internal sandbox operator returns a zip:
+
+```powershell
+powershell -NoProfile -ExecutionPolicy Bypass -File scripts\validate-returned-send-file-sandbox-package.ps1 -ZipPath <returned-zip> -Strict
+```
+
+The validator checks only sanitized booleans/counts/metadata:
+
+- target fields are present;
+- `ISPHERE_SEND_FILE_ALLOWED_DIR` is recorded;
+- `sandbox_file_path`, `file_sha256`, `file_size_bytes`, and `idempotency_key` are present;
+- before and after recorder output exists;
+- operator timestamps are present;
+- file upload/sent-record evidence is present;
+- duplicate second file send was not attempted;
+- `production_file_send_enabled=false`.
+
+## Current status
+
+No returned R9 package has been reviewed in this repository state.
+
+`isphere_send_file` remains preview/idempotency/audit only:
+
+- `send_file_preview_tool_present=true`
+- `send_file_duplicate_detected=true`
+- `send_file_conflict_blocked=true`
+- `send_file_production_enabled=false`
+
+## Next decision
+
+If a returned package passes `strict_file_gate_pass`, the next implementation round may design a gated file-upload connector path.
+
+If no returned package is available, keep file sending at preview only and continue local-safe rounds.