feat(agent): add clipboard image support

[Greg Lamberson (glamberson)]

Extends the daemon clipboard-get/clipboard-set operations added in #1863 to
images: clipboard-get-image writes the last image received from the remote
clipboard to a PNG file, clipboard-set-image reads a PNG file and advertises
it to the remote as CF_DIB/CF_DIBV5.

The daemon stores images as PNG bytes and converts to/from the wire's DIB
byte layout via ironrdp-cliprdr-format's existing png_to_cf_dib(v5) and
dib(v5)_to_png, so no new pixel-format code is needed here. Both DIB variants
are advertised when offering an image (DIBV5 is richer but not every peer
understands it); on paste, DIBV5 is preferred over DIB, and image is
preferred over text when the remote offers both.

Replaces ClipboardState's two Option fields with a small
ClipboardContent enum (Text/Image) so local and remote clipboard content is
a single logical item, matching how each clipboard-set* call replaces
whatever was there before. Adds a PendingPaste field to the CLIPRDR backend
to track which format was requested, since FormatDataResponse does not
itself carry the format it answers and MS-RDPECLIP allows only one
outstanding request at a time.

New Request::ClipboardGetImage/ClipboardSetImage and
Payload::ClipboardImage wire variants, bounded at 64 MiB (matching
ironrdp-cliprdr-format's own internal cap) both in the CLI parser and on
wire decode. clipboard_set_image validates the PNG up front by attempting
the DIB conversion, so a bad set fails immediately rather than only once the
remote asks for it.

Adds the two new variants to ironrdp-activex's exhaustive match on Request,
same treatment as the existing ClipboardGet/ClipboardSet arm (unavailable
through the ActiveX automation surface). Adds wire round-trip and
Debug-redaction test coverage for all four clipboard Request/Payload
variants, including the two existing text ones that had none before.

Behavior change: clipboard-get now prints (empty) if the last remote copy
was an image rather than text, since local/remote content is a single
logical item. Previously it always reflected the last text.

Known limitation: FormatDataResponse does not carry a request-correlation
ID, so a stale response to a superseded paste request (a second remote
copy landing before the first paste response arrives) is fed through
whatever PendingPaste variant is current at the time. The failure mode is
graceful: the mismatched conversion (dib_to_png/dibv5_to_png on the wrong
byte layout) returns an error and the response is dropped, not
misinterpreted as valid data.

cargo xtask check fmt/lints/tests/typos/locks all pass, including new wire
round-trip and Debug-redaction coverage for both DIB and DIBV5 paths. Not
yet verified against a live remote client; that check is still owed before
merge.

[Greg Lamberson (glamberson)]

Two PRs are stacked on this: #1878 (HTML support) is filed against master with a cumulative diff, since GitHub-native stacked PRs are not usable across a fork boundary. #1878 depends on the ClipboardContent enum introduced here.

[Benoît Cortier (CBenoit)]

LGTM! I’m trying out the new helmcode-based reviewer on this PR, but the code is looking good to me.

[Copilot]

🟡 Changes recommended

RPC size mismatch, stale-response correlation, and concurrent advertisement races can break clipboard operations.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds PNG clipboard image support to the agent daemon and CLI using CLIPRDR DIB conversions.

Changes:

• Adds image clipboard RPC variants and CLI commands.
• Supports DIB/DIBV5 advertisement and conversion.
• Adds wire round-trip and redaction tests.

File summaries

File	Description
crates/ironrdp-testsuite-extra/tests/agent.rs	Extends RPC codec tests.
crates/ironrdp-rpc/src/wire/mod.rs	Adds optional byte encoding.
crates/ironrdp-rpc/src/ipc.rs	Defines image RPC messages and limits.
crates/ironrdp-daemon/src/daemon.rs	Handles image clipboard requests.
crates/ironrdp-daemon/src/clipboard.rs	Implements DIB image clipboard behavior.
crates/ironrdp-daemon/Cargo.toml	Adds the format-conversion dependency.
crates/ironrdp-agent/src/help.rs	Documents image commands.
crates/ironrdp-agent/src/cli.rs	Implements image file operations.
crates/ironrdp-activex/src/rpc.rs	Marks image operations unavailable.
Cargo.lock	Records the dependency update.

Review details

• Files reviewed: 9/10 changed files
• Comments generated: 6
• Review effort level: Balanced