Add Compaction Resilience principle

[rhoegg]

Adds a fifth canonical principle, Compaction Resilience, as docs/principles/compaction_resilience.md, with a matching entry in the principles README.md index. Proposed and discussed in #4.

Substantive case

Context auto-compaction is a property of the agent runtime, not of any domain or adopter. Any sufficiently long agent task crosses the boundary, and at that boundary an agent that has treated its context window as the source of truth tends to reconstruct deliverables from discarded context (memory) rather than observed reality — producing confident-sounding but fabricated results. This principle makes reality-based reporting structurally easier than memory-based reporting: treat impending compaction as a checkpoint, not a cliff; commit and push before the boundary; write resumption state to a durable, in-git location; and resume from committed artifacts rather than conversation history.

It fits this repository's scope (canonical agent-coordination principles for the git-coordinated model) and leans on the substrate the model already assumes — coordination state is git state — so it sits alongside the existing four rather than expanding scope into tooling or new layer concepts.

It composes with the current principles rather than overlapping them:

• it is Hard Evidence applied across time to the agent's own memory (a post-compaction "I did X" from memory is not evidence; the committed artifact is);
• a cold resume is State Preconditions applied to oneself (verify the recorded SHAs/branch before building on them; a mismatch halts);
• it closes the Disclosure Is Not Correction failure where an agent writes a confident summary from wiped memory under context pressure, sometimes wrapped in an honest-sounding "from memory" caveat.

Provenance and shape

Proven at operator scope before this proposal (an operator umbrella has been running it as an Origin=self principle, with two tenants inheriting it in reference mode), so it is a validated pattern rather than a speculative one. The file follows the repository's file shape — title, one-paragraph scope note, generic canonical text with no operator- or tenant-specific examples.

Closes #4 on merge. As maintainer-owned, the merge decision rests with the maintainer; happy to adjust the text in review.