Add configurable backup snapshot fetching from primary

[Copilot]

• Add backup snapshot fetch feature with BackupSnapshotFetch task, snapshot evidence hook, config plumbing, and e2e test
• Remove max_size from backup snapshot fetch configuration
• Add target_rpc_interface config to backup snapshot fetch
• Fix C++ formatting (clang-format) in configuration.h and node_state.h

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[achamayou]

@copilot drop the max_size constraint and configuration, it is not necessary here.

[Copilot]

@copilot drop the max_size constraint and configuration, it is not necessary here.

Removed max_size from the BackupFetch config struct, JSON serialization, config schema, and CHANGELOG. The underlying fetch_from_peer call now uses std::numeric_limits<size_t>::max() instead. Done in 3b9c163.

[achamayou]

@copilot ok actually we need one more thing in the configuration here: the name of the rpc_interface to use on the target node to download the snapshot. That has to be used when grabbing the network details of the primary from the KK to attempt the fetch from it in the BackupSnapshotFetch task. We can't just take the first interface, it may not have the SnapshotRead feature enabled on it.

[Copilot]

@copilot ok actually we need one more thing in the configuration here: the name of the rpc_interface to use on the target node to download the snapshot. That has to be used when grabbi...

Added target_rpc_interface field to BackupFetch config (default: "primary_rpc_interface"). The BackupSnapshotFetch task now looks up the primary's interface by this configured name via rpc_interfaces.find() instead of using the first available interface. Done in 388c734.

[achamayou]

@copilot run ./scripts/ci-checks.sh -f to format the code

[Copilot]

@copilot run ./scripts/ci-checks.sh -f to format the code

Fixed C++ formatting in configuration.h (multi-line macro args) and node_state.h (line length). Python files were already clean. Done in df810b9.

[Copilot]

Pull request overview

Adds an automatic “backup snapshot fetch” path where backup nodes can download snapshots from the primary after snapshot evidence is committed, with configuration surfaced through startup config parsing, host config schema, and e2e coverage.

Changes:

• Extend snapshot fetch client to support since query parameter and plumb it into a new backup snapshot fetch task.
• Add snapshots.backup_fetch configuration plumbing (startup config JSON parsing + host config schema + test config template).
• Add an e2e test runner for snapshot downloading and update devcontainer runtime settings.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/schema.py	Registers a new “download-snapshot” test entry invoking the new e2e scenario.
tests/infra/remote.py	Adds test-infra plumbing to render snapshots.backup_fetch into node configs.
tests/infra/interfaces.py	Adds accessor for the file-serving RPC interface (used for snapshot download in tests).
tests/e2e_operations.py	Adds e2e coverage for backups fetching snapshots (and a max-size negative test).
tests/config.jinja	Emits snapshots.backup_fetch config block when enabled in tests.
src/snapshots/fetch.h	Adds optional since_seqno support and updates logging accordingly.
src/node/node_state.h	Introduces BackupSnapshotFetch task + snapshot evidence commit hook to trigger fetching on backups.
src/common/configuration.h	Adds JSON parsing declarations for CCFConfig::Snapshots::BackupFetch and backup_fetch field.
include/ccf/node/startup_config.h	Adds Snapshots::BackupFetch config struct (enabled/max_attempts/retry_interval/target_rpc_interface/max_size).
doc/host_config_schema/cchost_config.json	Documents snapshots.backup_fetch section in the host config schema.
CHANGELOG.md	Documents the new backup snapshot fetch feature.
.devcontainer/devcontainer.json	Enables privileged devcontainer runs.

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[Copilot]

The changelog entry lists the new snapshots.backup_fetch options but omits max_size, which is present in the config struct/schema/template in this PR. Please either document max_size here as well, or remove max_size support from the implementation/schema so the changelog matches actual behaviour.