feat: sign a canister call for submission from another machine

CHANGELOG.md

@@ -2,7 +2,8 @@
 Convention: changes to experimental features live in a dedicated
 `## Experimental` subsection under each version. Experimental features
 may receive breaking changes between releases without a major version
-bump. Currently experimental: project bundling, project dependencies
+bump. Currently experimental: project bundling, project dependencies,
+air-gapped signing
 -->
 
 # Unreleased
@@ -11,6 +12,12 @@ bump. Currently experimental: project bundling, project dependencies
 * feat: `icp completions <SHELL>` prints a shell completion script for `bash`, `zsh`, `fish`, `powershell`, or `elvish` to stdout. See the [installation guide](docs/guides/installation.md#shell-completions) for where to put it.
 * fix: `icp canister logs` output formats are corrected. `--json` now emits machine-readable JSON and the default emits the human-readable lines (the two were swapped), and `--follow --json` emits newline-delimited JSON, one record per line, streamed as each record arrives. This is breaking for scripts: parsing the default output as JSON now requires `--json`, and consumers of `--follow --json` must read one JSON object per line.
 
+## Experimental
+
+* feat(signing): `icp canister call --sign-only <FILE>` composes and signs a call and writes it to a JSON file instead of submitting it, so a machine that holds the key can prepare a call with no network at all and a machine with network can submit it without holding the key. `-` writes to stdout. Nothing is fetched while signing: the Candid interface comes from `--candid` or from the canister's local build artifact rather than from the canister itself, and `--root-key` must name a key (`mainnet` or a hex-encoded key) rather than `fetch`. `--proxy` is not supported. The command that submits the file, `icp message send`, follows separately.
+  * `--valid-from <WHEN>` places the message's submission window, as a duration from now (`55m`, `2h`) or an RFC 3339 timestamp; it defaults to now. The window is always five minutes wide, because the IC rejects an ingress message whose expiry is further ahead than that — so this places the window rather than sizing it. Note that this is not dfx's `--expire-after`, which names the window's *end* and leaves you to subtract the five minutes yourself.
+  * The file records the signed envelope, where to submit it, a tagged canister-or-subnet destination, the Candid interface, and a human-readable summary of what was signed. An update also carries a pre-signed `request_status` read, so the submitting machine can await the outcome with no key of its own; it shares the call's expiry, so both live in the same window.
+
 # v1.3.0
 
 * feat: a canister environment variable's value can now be read from a file, by writing `var: { path: <file> }` in place of `var: value`. The path resolves against the canister's directory — including in an environment override, matching `init_args` — and surrounding whitespace is trimmed off the file's contents. The file is read when the project is loaded, so a missing file fails before anything is deployed. `icp project bundle` writes the value into the bundled manifest inline, rejecting a file outside the project as it does for other manifest file references.

Cargo.toml

@@ -94,6 +94,7 @@ send_ctrlc = "0.6"
 semver = "1"
 serial_test = { version = "3.2.0", features = ["file_locks"] }
 serde = { version = "1.0", features = ["derive"] }
+serde_cbor = "0.11.2"
 serde_json = "1.0"
 serde_yaml = "0.9.34"
 sha2 = { version = "0.11.0", features = ["zeroize"] }
@@ -104,7 +105,7 @@ sysinfo = "0.38.4"
 tar = "0.4.46"
 tempfile = "3"
 test-tag = "0.1"
-time = { version = "0.3.47", features = ["formatting", "macros"] }
+time = { version = "0.3.47", features = ["formatting", "macros", "parsing"] }
 tiny-bip39 = "2.0.0"
 tokio = { version = "1.45.0", features = ["macros", "rt-multi-thread"] }
 tracing = "0.1.41"

crates/icp-cli/Cargo.toml

@@ -90,6 +90,7 @@ cryptoki.workspace = true
 predicates.workspace = true
 rand.workspace = true
 send_ctrlc.workspace = true
+serde_cbor.workspace = true
 serde_yaml.workspace = true
 serial_test.workspace = true
 test-tag.workspace = true