Fix #439: Add StringToStringCorrection model

[GiggleLiu]

Summary

Add the StringToStringCorrection problem model — a classical NP-complete satisfaction problem from Garey & Johnson (A4 SR20) concerning minimum-cost string transformation using only deletions and adjacent swaps.

Fixes #439

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.16%. Comparing base (6d2981d) to head (0db6b71).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #675      +/-   ##
==========================================
+ Coverage   97.15%   97.16%   +0.01%     
==========================================
  Files         300      302       +2     
  Lines       39753    39923     +170     
==========================================
+ Hits        38621    38791     +170     
  Misses       1132     1132              

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[GiggleLiu]

Implementation Summary

Changes

• New: src/models/misc/string_to_string_correction.rs — Model implementation (struct, constructor, Problem/SatisfactionProblem traits, declare_variants!, canonical example, ProblemSchemaEntry)
• New: src/unit_tests/models/misc/string_to_string_correction.rs — 11 unit tests (creation, evaluation, invalid ops, invalid-after-deletion, serialization, solver, paper example, unsatisfiable, identity, empty strings, delete-only)
• Modified: src/models/misc/mod.rs, src/models/mod.rs — Module registration and re-export
• Modified: src/unit_tests/trait_consistency.rs — Added check_problem_trait entry
• Modified: problemreductions-cli/src/cli.rs — Added --source-string, --target-string flags
• Modified: problemreductions-cli/src/commands/create.rs — Added StringToStringCorrection creation support
• Modified: docs/paper/reductions.typ — Display name + problem-def with figure showing operation trace
• Modified: docs/paper/references.bib — Added Wagner 1974, 1975 references
• Regenerated: src/example_db/fixtures/examples.json, docs/src/reductions/problem_schemas.json, docs/src/reductions/reduction_graph.json

Deviations from Plan

• None

Open Questions

• None

[Copilot]

Pull request overview

Adds a new NP-complete satisfaction problem model, StringToStringCorrection, to the problemreductions model registry and CLI, including examples and documentation updates, to address issue #439.

Changes:

• Introduce StringToStringCorrection model with schema registration, variant declaration, evaluation logic, and example-db spec.
• Add unit tests and example fixtures for the new model.
• Integrate the model into the CLI (pred create) and regenerate docs JSON + paper references/definition section.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/models/misc/string_to_string_correction.rs	New model implementation, schema registration, variant declaration, and example-db spec
src/models/misc/mod.rs	Export and include the new misc model + example-db spec aggregation
src/models/mod.rs	Re-export StringToStringCorrection from the top-level models module
src/unit_tests/models/misc/string_to_string_correction.rs	New unit tests covering creation, evaluation, invalid ops, serialization, and brute-force solving
src/unit_tests/trait_consistency.rs	Add trait consistency check coverage for the new model
src/example_db/fixtures/examples.json	Add example instance + sample/optimal configs for StringToStringCorrection
problemreductions-cli/src/cli.rs	Add --source-string / --target-string flags and update help text
problemreductions-cli/src/commands/create.rs	Add pred create StringToStringCorrection ... parsing and example string
docs/src/reductions/problem_schemas.json	Add generated schema entry for the new model
docs/src/reductions/reduction_graph.json	Add generated graph node entry for the new model and adjust indices
docs/paper/references.bib	Add Wagner (1974/1975) references used by the paper
docs/paper/reductions.typ	Add paper definition + example figure block for String-to-String Correction

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[GiggleLiu]

Agentic Review Report

Structural Check

#	Check	Status
1	Model file exists (src/models/misc/string_to_string_correction.rs)	PASS
2	inventory::submit! present	PASS
3	#[derive(...Serialize, Deserialize)] on struct	PASS
4	Problem trait impl	PASS
5	SatisfactionProblem impl	PASS
6	#[cfg(test)] + #[path = "..."] test link	PASS
7	Test file exists (src/unit_tests/models/misc/string_to_string_correction.rs)	PASS
8	Test file has >= 3 test functions	PASS — 14 test functions
9	Registered in misc/mod.rs	PASS
10	Re-exported in models/mod.rs	PASS
11	declare_variants! entry exists	PASS — default sat StringToStringCorrection => "(2 * source_length + 1) ^ bound_k"
12	CLI resolve_alias entry	PASS — registry-driven via inventory::submit!
13	CLI create support	PASS — --source-string, --target-string, --bound, optional --alphabet-size
14	Canonical model example registered	PASS — aggregated through misc/mod.rs into model_builders.rs
15	Paper display-name entry	PASS — "StringToStringCorrection": [String-to-String Correction]
16	Paper problem-def block	PASS — full problem-def with example figure

Issue Compliance (#439):

#	Check	Status
1	Problem name matches issue	OK
2	Mathematical definition matches	OK
3	Problem type (opt/sat) matches	OK — satisfaction (Metric = bool)
4	Type parameters match	OK — none, as specified
5	Configuration space matches	OK — vec![2 * source.len() + 1; bound_k]
6	Feasibility check matches	OK
7	Objective function matches	N/A — satisfaction problem
8	Complexity matches	OK — "(2 * source_length + 1) ^ bound_k"

Semantic Review:

• evaluate(): Correctly simulates the operation sequence on a working copy; handles delete/swap/no-op with proper boundary tracking. Early exits for structurally impossible instances.
• dims(): Correct — vec![2 * source.len() + 1; bound_k].
• Edge cases: Tested for empty strings, identity, unsatisfiable, target longer than source, excessive deletions, invalid operations after deletions.
• Complexity string represents brute-force enumeration (appropriate — no better algorithm known for general swap-and-delete variant; documented in paper footnote).
• Whitelist fail is expected: CLI help text, args, create logic, and CLI tests are standard for a model with full CLI support.

Build: make test PASS, make clippy PASS.

Structural summary: 16/16 checks passed, 8/8 issue compliance passed, no blocking issues.

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Quality Check

Design Principles:

Principle	Status	Notes
DRY	Minor issues	See below
KISS	OK	Straightforward model implementation
HC/LC	OK	Clean separation of concerns

HCI (CLI changes):

Aspect	Status	Notes
Error messages	OK	Actionable messages with flag names and usage examples
Discoverability	OK	Listed in --help for both create and solve
Consistency	OK	Flag naming follows existing conventions
Least surprise	OK	Piped examples show --solver brute-force
Feedback	OK	No silent failures

Test Quality: OK — 14 unit tests with concrete value assertions, boundary/adversarial coverage, full brute-force enumeration in paper example test, plus 4 CLI integration tests.

Issues (all minor):

1. DRY: Alphabet-size inference/validation duplication — create.rs:1580-1593 and 1512-1526 share near-identical logic between SCS and STSC handlers. A shared helper would reduce drift risk.
2. DRY: Symbol index parsing closure — create.rs:1570-1577 duplicates the inner loop of SCS handler. A reusable parse_comma_separated_usize() helper would be a small improvement.
3. Test: Missing --alphabet-size validation CLI test — The handler validates alphabet-size is not smaller than inferred, but no CLI test exercises this error path.
4. Docs: STSC pipe example inconsistency — docs/src/cli.md:302 uses piping (| pred solve -) instead of -o file.json pattern used by neighboring entries.

Quality summary: No critical or important issues. 4 minor suggestions.

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Agentic Feature Tests

#	Test	Command	Result
1	Catalog presence	pred list	PASS — StringToStringCorrection * appears with correct complexity
2	Details display	pred show StringToStringCorrection	PASS — description, complexity, 4 fields, 0 reductions
3	Example creation	pred create --example StringToStringCorrection	PASS — valid JSON output
4a	Solve (ILP, expected fail)	pred solve stsc.json	PASS — correct "no reduction path" error with --solver brute-force hint
4b	Solve (brute-force)	pred solve --solver brute-force stsc.json	PASS — solution [5, 7] manually verified correct
5	Create with CLI flags	pred create StringToStringCorrection --source-string "0,1,2,3,1,0" --target-string "0,1,3,2,1" --bound 2	PASS — infers alphabet_size=4
6	Create-pipe-solve	pred create ... | pred solve - --solver brute-force	PASS — end-to-end pipeline works
7	Edge: identity	source=target, bound=0	PASS — empty solution
8	Edge: unsatisfiable	bound=0, source != target	PASS — "No solution found"
9	Edge: empty strings	source=[], target=[]	PASS — trivially satisfied
10	Edge: swap only	source=[0,1,2], target=[1,0,2]	PASS — correct swap solution
11	Explicit --alphabet-size	--alphabet-size 5	PASS — overrides inferred value
12	Unit tests	cargo test --lib string_to_string_correction	PASS — 14/14
13	Full test suite	cargo test	PASS — all tests
14	CLI integration tests	cargo test -p problemreductions-cli --test cli_tests	PASS — 185/185
15	Clippy	cargo clippy --workspace	FAIL (minor) — unreachable pattern at create.rs:239, duplicate "Vec<u64>" match arm
16	Format check	cargo fmt --check	FAIL (minor) — formatting diff in cli_tests.rs:38

Confirmed issues:

1. Unreachable pattern (create.rs:239): Duplicate "Vec<u64>" match arm — second arm is dead code. Severity: low. Fix: remove duplicate arm or merge.
2. Formatting diff (cli_tests.rs:38): assert! call needs line wrapping per nightly rustfmt. Severity: low. Fix: cargo +nightly fmt.

Agentic test summary: All functional tests PASS. 2 minor lint/format issues confirmed.

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