feat: Add --no-create flag to icp deploy

[adamspofford-dfinity]

No description provided.

[Copilot]

Pull request overview

Adds an intended --no-create safeguard to icp deploy.

Changes:

• Adds missing-canister validation.
• Documents the flag in the changelog.
• Regenerates the CLI reference, but leaves it truncated.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
crates/icp-cli/src/commands/deploy.rs	Adds deployment guard logic.
CHANGELOG.md	Announces the new flag.
docs/reference/cli.md	Updates generated CLI documentation.

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[marc0olo]

This looks solid overall — clean implementation, good test coverage (both the missing and already-exists paths), and CHANGELOG + CLI docs are updated. 👍

Leaving final approval to Linwei/Raymond since this introduces a new flag.

A few optional, non-blocking nits:

1. Creating canisters: is logged unconditionally at deploy.rs:181, so the --no-create failure prints Creating canisters: immediately followed by the "will not create" error, which reads a little oddly. Could move that log into the else create branch.
2. Suppressing the All canisters already exist message under --no-create is a minor special case — deploy proceeds identically either way when everything exists, so leaving it unconditional would be simpler.
3. Not a request to change here, just noting: the build runs before the --no-create check, so the flag doesn't fail-fast before building. Fine given the check needs the env/agent/ids.

None of these block merge.

[lwshang]

• Reworded the phase header "Creating canisters:" → "Ensuring canisters exist:". The old header over-claimed — it printed even when nothing would be created, reading oddly ahead of both "All canisters already exist" and the new --no-create error. The new wording reads naturally everywhere, and "All canisters already exist" now prints unconditionally again.
• Made --no-create conflict with --subnet/--cycles at parse time (with a test). They only affect creation, so combined with --no-create they were silently ignored — now clap rejects the combo up front. --proxy is left out since it's used beyond creation.