v1.0.0

Changelog

Arc follows semantic versioning. What that covers, and what it does not, is
described under Compatibility.

1.0.0

The first stable release. Everything below already existed across the 0.x
series; 1.0 is the point at which the command line, the configuration file, the
remote protocol and the stored formats become things you can depend on.

Stable

• Local execution cache. arc run -- <command> fingerprints the command,
  its arguments, its working directory, the configured environment variables and
  everything it is known to depend on. A hit restores the recorded output and
  exit status instead of running the command.
• Dependency intelligence. Arc observes what a command reads, stats,
  enumerates and executes, and narrows the next run's fingerprint to exactly
  that — but only when it can prove the observation was complete.
• Task graph. Producer/consumer edges are learned from what tasks actually
  read and write. arc graph shows it; arc affected uses it.
• Selective execution. arc affected --run executes what a change reaches
  and nothing else, in dependency order, with bounded parallelism.
• Shared cache. A content-addressed store over HTTP, with digest
  verification on every object before it becomes local state.
• CI integration. arc ci determines the work a branch requires, reuses
  what the shared cache already holds, and reports what was reused.
• Remote execution. Cache misses can be sent to a worker. Results are
  published only after every artifact is uploaded and verified.
• Execution environments. Content-addressed, immutable toolchain bundles
  that participate in the execution key, so a toolchain change cannot hit.
• Linux tracing. Two backends: linux-seccomp, which uses seccomp user
  notification and needs no privilege, and linux-ptrace, which remains the
  fallback and the reference. See docs/tracing.md.

Experimental

• Remote execution end-to-end deployment. The mechanism is tested and its
  correctness contract is defined, but the reference server has no
  authentication and must not be exposed to an untrusted network. See
  docs/security.md.

Platforms

	tracing	narrowing	cache	remote	environments
Linux x86-64	seccomp / ptrace	yes	yes	yes	yes
Linux aarch64	seccomp / ptrace	yes	yes	yes	yes
Windows x86-64	snapshot + job object	no	yes	yes	yes
macOS	snapshot	no	yes	yes	yes

Only platforms exercised by CI are listed as supported. Where a platform cannot
observe reads, Arc does not narrow: it falls back to the conservative project
scan, which is slower and always correct.

Known limitations

• Automatic narrowing is Linux-only. Windows and macOS use the conservative
  project scan.
• no_new_privs is required by the seccomp backend, so a setuid program in a
  traced tree does not gain its extra privilege. Arc documents this rather than
  working around it.
• Environment variable reads cannot be observed by any syscall tracer. Arc uses
  the configured variable set instead.
• Shared memory and message queues are not modelled.

Compatibility

Covered by semantic versioning from 1.0.0 onwards:

• the command line: command names, flags, defaults and exit codes
• arc.toml keys and their meanings
• --json output field names and meanings
• the remote cache and remote execution wire protocols
• stored cache records, to the extent that a newer Arc reads an older one

Not covered:

• the Rust API of arc-core, arc-cache and arc-worker. These are internal
  crates published only because the binaries need them. Their public items are
  pub for visibility, not as an API promise.
• human-readable terminal output, which is formatting rather than interface.

An older Arc reading newer local metadata rebuilds rather than misreading.
Downgrading is not tested and is not supported.

Earlier releases

The 0.x series was developed as a sequence of milestones — local cache,
dependency intelligence, task graph, shared cache, CI, remote execution,
environments, fast tracing — and did not carry compatibility guarantees between
them. Their history is in the git log.