fix(parser): bound the interposed defender-exception class at a sentence terminator (#9266)

[luckenbach]

Closes #9266. Follow-up from #8785 / PR #9201.

The defect

defender_exception_ir locates the interposed player class with
scan_preceded, which walks forward to the first position where
"as though <pronoun> didn't have defender" parses and treats everything
before it as the class. Nothing stopped that walk stepping over a sentence
terminator, so a card whose later sentence printed the tail would have the
first sentence's remainder swallowed into the "class".

Containment was empirical — no corpus card prints that shape — and the
failure is fail-closed: an unrecognized class becomes
static_helpers::unenforceable_gate_marker, so the permission is withheld and
the card shows red in coverage rather than granting something wrong. This
change makes the containment structural: a property of the grammar rather
than of the current card pool.

Where the bound went, and why not inside the scan

The issue suggested bounding the scan "before the tail predicate is
attempted". I implemented it instead as a validation of the materialized
segment, one line after scan_preceded returns:

all_consuming(opt(is_not::<_, _, VE>("."))).parse(segment)?;

The two are behaviourally equivalent on this path — scan_preceded returns
the earliest match, so a tail inside sentence one yields a non-spanning
segment either way, and a tail only in a later sentence is refused either way.
The reason to prefer the local check is blast radius: scan_preceded is a
shared primitive with 155 call sites across 23 parser files, and threading
a stop condition through it would put every one of those on the diff for a
defect that lives at one call site.

What the test does and does not cover

interposed_class_may_not_span_a_sentence_boundary is four-sided, because
the risk a boundary check introduces is over-rejection. One fixture asserts
the refusal; three are controls asserting that the unrestricted form, a
populated single-sentence class, and a terminator after the tail all still
parse and still classify.

Mutation results, three-way classified:

Mutation	Result
Remove the bound entirely	DISCRIMINATES — reds a segment spanning a sentence terminator must be refused
Drop the opt wrapper	VACUOUS — every fixture stays green

The second row is recorded in the source rather than quietly dropped. An
earlier revision of this change claimed the unrestricted fixture protects the
opt; that was false — scan_preceded advances past the leading space, so the
segment on this path is " " rather than "" and is_not matches it with or
without the wrapper. Both the production comment and the test doc now say the
wrapper is defensive-only and that no row here discriminates it, instead of
crediting it to a fixture that does not.

Verification

• cargo fmt --check clean

• Gate A (parser-combinator scan) PASS; Gate P (PreLowered ratchet) PASS

• lib: 22062 passed, 0 failed

• integration: 7664 passed, 0 failed

• clippy, CI's exact line
  (--locked --workspace --exclude phase-tauri --all-targets --features engine/proptest -- -D warnings):
  0 errors, exit 0

• Card impact: 0 cards, measured — not inherited from the issue's
  "no corpus card has this shape" claim.

  oracle-gen built and run at base d471a63cf and candidate 1836288aa
  in detached worktrees against one pinned MTGJSON vintage
  (MTGJSON_SKIP_REFRESH=1). Both sides gated: is_not absent from
  defender_exception.rs at base, present at candidate. 35943 faces each
  side, 92.0% coverage each side. Diffed in three directions so a card
  added by the change cannot hide — removed 0, added 0, changed 0.

  Read precisely: this says the change moves no card in the current corpus,
  which is the expected result for a refusal targeting a shape no card
  prints. It is not independent evidence that the bound fires — that is what
  the M1 mutation above buys.

All figures above were produced against the committed candidate 1836288aa
with a clean tree, not against a working tree that was edited afterwards.

Unrelated observation, not addressed here

While checking this branch I ran clippy with --all-features rather than CI's
line, and crates/engine/src/database/forge/ fails to compile — 14 errors
(E0063/E0308/E0559) from struct fields and variants the types::ability types
have gained since. I confirmed this is pre-existing: base d471a63cf
produces the identical 14 errors. CI never builds it, because its clippy line
passes --features engine/proptest and the forge feature is off. Flagging it
rather than fixing it — out of scope for this PR, and worth its own issue if
the Forge bridge is still meant to build.

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Summary by CodeRabbit

• Documentation
  • Updated the implementation comment and test documentation to describe the sentence-boundary rule without the CR 702.3b prefix.

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📝 Walkthrough

Walkthrough

The implementation comment and test documentation no longer include the CR 702.3b prefix. No behavior change is described in the supplied diff summary.

Changes

Sentence-boundary comment update

Layer / File(s)	Summary
Update sentence-boundary references crates/engine/src/parser/oracle_nom/defender_exception.rs	The implementation comment and test documentation no longer include the CR 702.3b prefix.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 9dd7f

No actionable merge-blocking issue is established; complete the pending checks before merging.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the primary parser change: bounding the interposed defender-exception class at a sentence terminator. It is specific and related to the stated PR objective.
Linked Issues check	✅ Passed	Issue #9266 requires structural containment of the interposed scan at sentence boundaries and a regression fixture. The whole-PR diff adds all_consuming(opt(is_not::<_, _, VE>("."))) after `scan_pre…
Out of Scope Changes check	✅ Passed	The changes are limited to defender_exception.rs. The production validation, regression tests, and parser comments directly support issue #9266. The final citation removal corrects comments for the …
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 1 files.

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Inline comments:
In `@crates/engine/src/parser/oracle_nom/defender_exception.rs`:
- Line 275: Remove the CR 702.3b citation from the boundary comments associated
with the `is_not(".")` check and its test. Describe only that the parser rejects
an interposed segment spanning sentences.

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[github-actions]

Generated for head 1f1292f4fdce516a77987f249c4dc7f7558883f7.

Parse changes introduced by this PR

✓ No card-parse changes detected.

[matthewevans]

Held on head 1836288aa561958c63bed37e0211c7a80bc48142. The parser boundary and its regression are reviewable, and this head's required CI and parse-diff receipt are green. The two new comments at crates/engine/src/parser/oracle_nom/defender_exception.rs:275,506 cite CR 702.3b for a sentence-boundary rule it does not state; CR 702.3b says only that a creature with defender can't attack.

I prepared a two-line, comment-only maintainer correction locally (9dd7f8e595) and confirmed formatting, the parser combinator/pre-lowered gates, and the CR-citation anchor hook. Tilt is unavailable for this checkout, so I have not pushed the correction or approved/enqueued the PR. Next step: run the relevant Tilt verification when available, push the correction to this branch, then review the new head's CI/parse receipt and enqueue if the full gate remains clean. No change is requested from the contributor for this small correction.

[luckenbach]

You're right, and thank you for catching it. CR 702.3b says only that a creature
with defender can't attack. It says nothing about sentence scope, and I attached
it to a claim it does not support at both defender_exception.rs:275 and :506.

Worth being precise about what the right fix is, since it affects your two-line
correction: I don't think there is a CR rule to swap in. "The interposed segment
is a player class, and a player class does not span sentences" is not a rules
statement at all — it's a grammar invariant about how Oracle text is written,
which is why no citation fits it. The honest repair is to drop the citation
from both comments rather than renumber it, and let the sentences stand as the
parsing claim they actually are. CR 702.3b is still correctly cited elsewhere in
that file for the thing it does say.

I've left the branch alone so your prepared 9dd7f8e595 applies cleanly — happy
to push the correction myself instead if that's easier than waiting on Tilt, just
say which you'd prefer.

For the record on the other half: the parse-diff receipt agreeing with the
0 cards figure in the description is an independent confirmation, not a restatement
— I measured it locally by building oracle-gen at base and head and diffing
card-data keys, and CI computed its own against the true merge base.

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[matthewevans]

Confirmed on head 1836288aa561958c63bed37e0211c7a80bc48142: the sentence boundary is a parser grammar constraint, and CR 702.3b does not state it. The prepared maintainer commit 9dd7f8e595 removes that citation from both comments without replacing it with another rule number. The branch is unchanged, so the correction remains directly applicable. I also see the independent current-head parse-diff receipt reporting zero card changes.

The hold remains in place because Tilt is still unavailable for verification. I will verify and push the comment-only correction when the relevant Tilt resources are available, then check the new head's CI and parse receipt before approval/enqueue. No contributor action is needed for this correction.

[matthewevans]

Held on head 9dd7f8e595a0fdc2e51f8b0b8569e644f8d61ee9. I verified that CR 702.3b addresses defender's attack restriction, while the two corrected comments describe a parser sentence boundary. The prepared comment-only maintainer fixup passed cargo fmt --all, git diff --check, and the standalone CR citation-anchor check, and I pushed it to this branch. No contributor action is needed.

GitHub has not reported checks or an exact-head parse-diff receipt for this new commit yet. I will recheck them, then approve and enqueue if the full review bar remains clear. The previous head's green CI does not verify this commit.

[matthewevans]

Held on head 1f1292f4fdce516a77987f249c4dc7f7558883f7. I merged current main into this branch in an isolated worktree and pushed the clean merge. The PR diff still changes only defender_exception.rs; the sentence-bound parser regression remains in place, the earlier CR citation finding is resolved, cargo fmt --all, git diff --check, and the parser combinator gate passed, and there are no textual merge conflicts.

GitHub's required checks for this new head are queued, and the parse-diff sticky still reports the previous head. I will recheck exact-head CI and the parse-diff receipt, then approve/enqueue if both complete cleanly and the review remains clear. No contributor action is needed while those receipts are pending.

[matthewevans]

Held on head 1f1292f4fdce516a77987f249c4dc7f7558883f7 pending exact-head Rust tests. The previous CI attempt compiled the Rust test archive but GitHub canceled its archive job before the test shards could run; the required Rust aggregate check therefore failed without a test result. Rust lint and card-data checks passed, and the parse-diff receipt now names this head and reports zero card changes.

I started a full rerun of CI run 36172269116, attempt 2. It is queued. I will check the Rust archive, shards, and required aggregate when the rerun settles, then approve and enqueue if the exact-head checks pass and the reviewed diff remains clean. If it fails, I will investigate the concrete failure. No contributor action is needed while the rerun runs.

[matthewevans]

Approved on 1f1292f4fdce516a77987f249c4dc7f7558883f7. The sentence-boundary check is at the existing defender-exception parser seam; its regression fails when the bound is removed, and the unrestricted and single-sentence controls remain accepted. The earlier CR 702.3b comment issue is corrected. Exact-head Rust, card-data, and required checks passed, and the parse-diff receipt reports zero card changes. No remaining blocking review finding.