feat(bsk): support drop to upload

crates/bsk-cli/skill/SKILL.md

@@ -210,18 +210,23 @@ Both capture from the moment the tab is attached and read a bounded per-tab buff
 
 | Command | Summary |
 |---------|---------|
-| `bsk upload <ref-or-selector> --file <path>` | Click one upload trigger and attach an agent-readable local file (`--file` is repeatable) |
+| `bsk upload <ref-or-selector> --file <path>` | Attach a local file through a file-input trigger; use `--mode drop` only for an explicit drop zone (`--file` is repeatable) |
 | `bsk download <ref-or-selector> --out <path>` | Click one download trigger and copy the single completed file to an exact local path (`--overwrite` is opt-in) |
 
 The agent/harness decides whether a file transfer is appropriate and which local path belongs to the task. Treat upload as disclosure of that file to the current website, and download as accepting website-controlled bytes onto the local filesystem. Use only paths that are necessary for the user's bounded goal.
 
-BrowserSkill enforces the mechanical boundary: files are staged under a session-scoped opaque transfer, only daemon-minted capabilities reach the extension, upload/download still obey Agent Window tab checks, and transfers are chunk/size bounded. Upload intercepts the native chooser for one transaction, locates the input activated in the resolved target's document, and assigns only the staged file paths. Download uniquely correlates one exact-target browser intent with one Chrome download in either event order, routes it through a daemon-minted relative directory, and lets the daemon validate and import it. Upload staging remains available for a later form submission and is removed when the session ends. Downloads cannot overwrite an existing destination unless `--overwrite` is explicit. BrowserSkill does not inspect file content or decide whether its meaning is sensitive.
+BrowserSkill enforces the mechanical boundary: files are staged under a session-scoped opaque transfer, only daemon-minted capabilities reach the extension, upload/download still obey Agent Window tab checks, and transfers are chunk/size bounded. The default upload mode intercepts one chooser transaction, locates the file input activated in the resolved target's document, and assigns only the staged paths. `--mode drop` does not click: it delivers the same staged files through one native browser drop bound to the explicitly resolved drop zone. These mechanisms never fall back to each other automatically. Download uniquely correlates one exact-target browser intent with one Chrome download in either event order, routes it through a daemon-minted relative directory, and lets the daemon validate and import it. Upload staging remains available for a later form submission and is removed when the session ends. Downloads cannot overwrite an existing destination unless `--overwrite` is explicit. BrowserSkill does not inspect file content or decide whether its meaning is sensitive.
+
+A successful drop command means Chrome dispatched the native file drop to the resolved zone; it does not prove that the site's application logic accepted the attachment. Observe the page once after the command, and do not repeat the drop when the attachment is already present.
 
 Do not use `request-help` merely because a native file chooser or browser download is involved; try these commands first. For transfer failures, use the structured error instead of retrying blindly:
 
 - `reason=file_input_not_activated` means the requested click did not activate exactly one `<input type="file">`; the page may use a non-input picker such as `window.showOpenFilePicker()`. Do not retry blindly. If human help is available, call `request-help` and tell the user the exact original local path to choose. The staged daemon path is internal and must not be shown to the user.
 - `reason=file_input_probe_failed` means BrowserSkill could not safely establish the browser-side upload transaction. Do not repeat the same action; use `request-help` when available.
 - `reason=set_file_input_failed` means BrowserSkill found the activated file input but Chrome rejected the staged path or assignment. Check the extension's file-URL access permission; otherwise use `request-help`.
+- `reason=upload_mechanism_unsupported` means the browser cannot perform a native file drop. Do not retry the same drop; use a standard file-input trigger or `request-help`.
+- `reason=file_drop_target_unavailable` means the specified point is no longer owned by the resolved drop zone. When `effect_state=none`, re-observe and select the visible drop zone itself; do not guess another target.
+- `reason=file_drop_failed` means the native drop command failed. Do not retry when `effect_state=unknown`; first observe whether the page already received the file.
 - `reason=download_capture_failed` means BrowserSkill could not attribute exactly one completed download to the requested target. Do not retry blindly or accept an unrelated browser download; use `request-help` when available.
 - `effect_state=none` means BrowserSkill confirmed that no file-transfer effect was committed. Follow the accompanying reason; a corrected target or explicit human fallback may be attempted.
 - `effect_state=unknown` means the browser may already have attached or created the file. Do not repeat the transfer. Observe the page if that can establish the result; otherwise stop and report the uncertainty.

crates/bsk-cli/src/cli/mod.rs

@@ -182,7 +182,7 @@ pub enum Command {
     /// Set `<select>` option values by `value` attribute.
     Select(SelectArgs),
 
-    /// Upload one or more local files through a page file chooser.
+    /// Upload files through a page file input or explicit drop target.
     Upload(UploadArgs),
 
     /// Capture one browser download and write it to a local path.

crates/bsk-cli/src/cli/render_error.rs

@@ -52,6 +52,9 @@ pub mod reason {
     pub const FILE_INPUT_PROBE_FAILED: &str = "file_input_probe_failed";
     pub const FILE_INPUT_NOT_ACTIVATED: &str = "file_input_not_activated";
     pub const SET_FILE_INPUT_FAILED: &str = "set_file_input_failed";
+    pub const UPLOAD_MECHANISM_UNSUPPORTED: &str = "upload_mechanism_unsupported";
+    pub const FILE_DROP_TARGET_UNAVAILABLE: &str = "file_drop_target_unavailable";
+    pub const FILE_DROP_FAILED: &str = "file_drop_failed";
     pub const DOWNLOAD_CAPTURE_FAILED: &str = "download_capture_failed";
     pub const TRANSFER_OUTCOME_UNKNOWN: &str = "transfer_outcome_unknown";
     pub const TRANSFER_TIMEOUT: &str = "transfer_timeout";
@@ -323,6 +326,30 @@ pub fn info_for_error(code: ErrorCode, data: Option<&serde_json::Value>) -> Rend
             ),
             exit_code: base.exit_code,
         },
+        (ErrorCode::Unsupported, reason::UPLOAD_MECHANISM_UNSUPPORTED) => RenderInfo {
+            summary: "the browser does not support native file-drop upload",
+            hint: Some(
+                "do not retry the same drop; use a standard file-input target or `bsk request-help`",
+            ),
+            exit_code: base.exit_code,
+        },
+        (
+            ErrorCode::PermissionDenied | ErrorCode::Timeout | ErrorCode::CdpFailed,
+            reason::FILE_DROP_TARGET_UNAVAILABLE,
+        ) => RenderInfo {
+            summary: "the file-drop target could not be safely resolved",
+            hint: Some(
+                "rerun observe and select the visible drop zone itself; no file was delivered when effect_state is none",
+            ),
+            exit_code: base.exit_code,
+        },
+        (ErrorCode::Timeout | ErrorCode::CdpFailed, reason::FILE_DROP_FAILED) => RenderInfo {
+            summary: "the browser could not complete the native file drop",
+            hint: Some(
+                "do not retry when effect_state is unknown; observe the page first, otherwise use `bsk request-help`",
+            ),
+            exit_code: base.exit_code,
+        },
         (ErrorCode::CdpFailed, reason::DOWNLOAD_CAPTURE_FAILED) => RenderInfo {
             summary: "the browser download could not be attributed or completed",
             hint: Some(
@@ -487,6 +514,29 @@ mod tests {
         );
         assert!(info.hint.unwrap().contains("do not retry"));
 
+        let unsupported_drop =
+            serde_json::json!({ "reason": reason::UPLOAD_MECHANISM_UNSUPPORTED });
+        let info = info_for_error(ErrorCode::Unsupported, Some(&unsupported_drop));
+        assert_eq!(
+            info.summary,
+            "the browser does not support native file-drop upload"
+        );
+        assert!(info.hint.unwrap().contains("standard file-input"));
+
+        let unavailable_target =
+            serde_json::json!({ "reason": reason::FILE_DROP_TARGET_UNAVAILABLE });
+        let info = info_for_error(ErrorCode::PermissionDenied, Some(&unavailable_target));
+        assert_eq!(
+            info.summary,
+            "the file-drop target could not be safely resolved"
+        );
+        assert!(info.hint.unwrap().contains("effect_state is none"));
+
+        let failed_drop = serde_json::json!({ "reason": reason::FILE_DROP_FAILED });
+        let info = info_for_error(ErrorCode::Timeout, Some(&failed_drop));
+        assert!(info.summary.contains("native file drop"));
+        assert!(info.hint.unwrap().contains("effect_state is unknown"));
+
         let download = serde_json::json!({ "reason": reason::DOWNLOAD_CAPTURE_FAILED });
         let info = info_for_error(ErrorCode::CdpFailed, Some(&download));
         assert!(info.summary.contains("download could not be attributed"));

crates/bsk-cli/src/cli/upload.rs

@@ -10,19 +10,35 @@ use base64::Engine;
 use bsk_protocol::Method;
 use bsk_protocol::tools::{
     TransferBeginParams, TransferBeginResult, TransferChunkParams, TransferChunkResult,
-    TransferIdParams, TransferReadyResult, TransferReleaseResult, UploadFile, UploadParams,
-    UploadResult,
+    TransferIdParams, TransferReadyResult, TransferReleaseResult, UploadFile, UploadMode,
+    UploadParams, UploadResult,
 };
-use clap::Args;
+use clap::{Args, ValueEnum};
 
 use crate::cli::ensure_daemon::ensure_daemon;
 use crate::cli::error::{CliError, Format};
 use crate::cli::interaction::split_target;
 use crate::cli::navigate::parse_timeout_ms;
 
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, ValueEnum)]
+pub enum UploadModeArg {
+    #[default]
+    Input,
+    Drop,
+}
+
+impl From<UploadModeArg> for UploadMode {
+    fn from(value: UploadModeArg) -> Self {
+        match value {
+            UploadModeArg::Input => Self::Input,
+            UploadModeArg::Drop => Self::Drop,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Args)]
 pub struct UploadArgs {
-    /// Snapshot ref (`@e3`) or CSS selector for the file input / chooser trigger.
+    /// Snapshot ref (`@e3`) or CSS selector for the chooser trigger / drop target.
     pub target: Option<String>,
     #[arg(long = "ref")]
     pub ref_: Option<String>,
@@ -31,6 +47,9 @@ pub struct UploadArgs {
     /// Local file to upload. Repeat for a multiple-file input.
     #[arg(long = "file", required = true)]
     pub files: Vec<PathBuf>,
+    /// Browser mechanism used to deliver the staged files.
+    #[arg(long, value_enum, default_value_t)]
+    pub mode: UploadModeArg,
     #[arg(long)]
     pub session: String,
     #[arg(long = "tab-id")]
@@ -73,6 +92,7 @@ pub fn dispatch(args: UploadArgs, format: Format) -> Result<(), CliError> {
                 staged_path: None,
             })
             .collect(),
+        mode: args.mode.into(),
         timeout_ms: Some(args.timeout),
     };
     let result = crate::cli::business_rpc::call::<_, UploadResult>(

crates/bsk-cli/tests/cli_parse.rs

@@ -6,6 +6,7 @@ use bsk::cli::daemon::{DaemonCmd, parse_duration};
 use bsk::cli::navigate::NavigateCmd;
 use bsk::cli::record::{RecordCmd, RecordSub};
 use bsk::cli::session::{SessionCmd, SessionSub};
+use bsk::cli::upload::UploadModeArg;
 use bsk::{Cli, Command};
 use clap::Parser;
 
@@ -13,6 +14,54 @@ fn parse(args: &[&str]) -> Cli {
     Cli::try_parse_from(args).expect("clap parse should succeed")
 }
 
+#[test]
+fn parses_upload_modes() {
+    let cli = parse(&[
+        "bsk",
+        "upload",
+        "@e1",
+        "--file",
+        "image.png",
+        "--session",
+        "s1",
+    ]);
+    let Command::Upload(default_args) = cli.command else {
+        panic!("expected upload subcommand");
+    };
+    assert_eq!(default_args.mode, UploadModeArg::Input);
+
+    let cli = parse(&[
+        "bsk",
+        "upload",
+        "@e1",
+        "--file",
+        "image.png",
+        "--session",
+        "s1",
+        "--mode",
+        "drop",
+    ]);
+    let Command::Upload(drop_args) = cli.command else {
+        panic!("expected upload subcommand");
+    };
+    assert_eq!(drop_args.mode, UploadModeArg::Drop);
+
+    assert!(
+        Cli::try_parse_from([
+            "bsk",
+            "upload",
+            "@e1",
+            "--file",
+            "image.png",
+            "--session",
+            "s1",
+            "--mode",
+            "auto",
+        ])
+        .is_err()
+    );
+}
+
 #[test]
 fn parses_daemon_start_with_defaults() {
     let cli = parse(&["bsk", "daemon", "start"]);