RFC-0005: filesystem host-surface plugin RFC (draft, bitty.fs successor)

[Xuepoo]

Priority: P1 | Area: architecture | Labels: docs,P1 | Milestone: v0.1.0 | RFC: OQ-056 | Issue: #439 | Task: CTX-0280

Draft successor RFC for the missing plugin file-access surface (RFC-0004 pattern: draft, security review, acceptance). Reconciles the draft illustrative bitty.fs.open/append/read/list sketch (panel-history candidate) against the accepted fs.read:PATTERN/fs.write:PATTERN capability split as decided verbs read/write/list under a NEW bitty.fs.* root (never bitty.terminal.*, v1 frozen with no fs namespace): scoped grants with no wildcard reusing the 4096/32/8KiB Core bounds, typed oracle-tight denials, untrusted labeling with preview-equality, read-into-VM-only grant combination, and no watch or tail-follow.

Targets OQ-056 (amended in this PR to name the surface as v2 scope, W-01/W-139 amendment pattern). No Closes: this PR must NOT merge until independent security review plus acceptance (commander arranges next). Blocked consumers: file-manager (draft policy-only), editor preview, Wheel (illustrative only).

Files: new docs/decisions/rfcs/RFC-0005-filesystem-host-surface.md (draft); OQ-056 amendment in docs/decisions/open-questions.md; rfcs/README.md table row; decisions/index.md candidate bullet. No implementation claims; no weakening of the accepted fs identifier split, the v1 freeze, or the Core-boundary rules.

Gates: just check exit 0; act -n dry-run of ci.yml success.

Note: the commit subject carries a [CTX-0279] prefix prepended by the managed prepare-commit-msg hook from stale branch binding (this work is CTX-0280 on branch ctx-0280/docs-rfc-0005-fs-surface). Amend cannot clear it (the hook re-adds it) and bypassing the hook is forbidden, so the artifact is disclosed here instead (same precedent as #431, #433, and #434).

Do NOT merge (commander merges after CI + CodeRabbit + security review).

[Xuepoo]

Security-review fixes applied (reviewer rfc0005-reviewer, PX-0931 NEEDS-FIX F-01..F-04) in 0b0bab1 — RFC file only, stays draft:

• F-01 (listing denial): listings now suppress denied entries silently (silent skip) as the default; any alternative shape is parked to the security review only if it preserves the no absent-vs-denied signal rule, with disposition required before acceptance. Unresolved question + threat-model touchpoint updated to match.
• F-02 (no migration): added explicit both-directions sentence — a terminal.* grant never implies an fs-family grant and vice versa — and named terminal input/output in the non-implication list.
• F-03 (label survival): label now survives redaction, truncation, and attribution.
• F-04 (combination rule): process invocation over file content now restates argv-first with validated arguments and no shell-string construction or interpolation (P0-AC-009) in the rule itself.

Gates: just check green. Not merged — awaiting re-review + acceptance.

[Xuepoo]

Mechanical acceptance flip for RFC-0005 (filesystem acceptance) pushed.

Commit: 5dc321a on ctx-0280/docs-rfc-0005-fs-surface (prev head 0b0bab1). Stale-hook prefix artifact [CTX-0281] disclosed (hook prepended [CTX-0281] to [CTX-0280] subject, same class as prior [CTX-0279] artifact on this branch).

Flips (no normative rewording, per PX-0936 list):

• docs/decisions/rfcs/RFC-0005-filesystem-host-surface.md: frontmatter status draft->accepted + description Draft->Accepted contract; header blockquote draft->accepted on 2026-10-05 with PR [CTX-0281] docs(security): add filesystem family matrix and P0-AC scope notes (RFC-0005 gate) #442 merge ref; UQ listing silent-suppression APPROVED disposition + UQ matrix [CTX-0281] docs(security): add filesystem family matrix and P0-AC scope notes (RFC-0005 gate) #442-satisfied disposition; Acceptance evidence appended paragraph with PX-0933/PX-0936/PX-0937, PR [CTX-0281] docs(security): add filesystem family matrix and P0-AC scope notes (RFC-0005 gate) #442 merge 856f34d, per-UQ dispositions (7).
• docs/decisions/rfcs/README.md: Draft->Accepted row.
• docs/decisions/index.md: Draft->Accepted bullet + frontmatter draft->accepted.
• docs/decisions/open-questions.md: OQ-056 Accepted 2026-10-05 for the filesystem dimension only note (OQ stays open).

Evidence verified:

• Security APPROVE PX-0933 (re-review 0b0bab1 F-01..F-04).
• Acceptance PX-0936 (NOT-YET conditional on curator, now satisfied).
• Curator APPROVE PX-0937 (fills PX-0936 gap).
• Matrix PR [CTX-0281] docs(security): add filesystem family matrix and P0-AC scope notes (RFC-0005 gate) #442 MERGED 2026-10-05T19:19:14Z, merge 856f34d (L0-L4 filesystem cells + P0-AC-035/030/024/013 scope notes, silent-skip default).
• SHAs resolve via git cat-file: 0b0bab1, 856f34d, d1267b6, 5dc321a.
• Links resolve via gh API: [P1] docs(rfc): filesystem host-surface plugin RFC (RFC-0005, bitty.fs successor) #439 OPEN, RFC-0005: filesystem host-surface plugin RFC (draft, bitty.fs successor) #440 OPEN at 5dc321a, [CTX-0281] docs(security): add filesystem family matrix and P0-AC scope notes (RFC-0005 gate) #442 MERGED.

Gates: just check exit 0 (fmt-check / markdownlint 0 issues / links 102 files / cross-repo offline 102 files 939 links 115 unique resolved 115 dead 0 / metadata / language / agents / hygiene / svg-skip / state / actionlint).

Not merged (commander merges after CI). Mergeable=MERGEABLE, mergeStateStatus=BLOCKED at push time.