diff --git a/docs/architecture.md b/docs/architecture.md
index d5f39de..0fe5c45 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -33,9 +33,11 @@ Implemented today:
 - Deterministic proposal-index assignment and enriched proposal mapping for shared generation.
 - Proposal-generation diagnostics artifacts with secret redaction.
 - Production module registry scaffolding with known-key recognition and explicit unsupported/unimplemented errors.
+- Production `grammar` module implementation in `internal/modules/grammar`.
+- Explicit runtime support for `--modules grammar` through the production runner path.
 
 Not implemented in CLI runtime path today:
-- Real module execution pipeline (`glossary`, `homophones`, `spoken_word`, `grammar`).
+- Real module execution pipeline for `glossary`, `homophones`, and `spoken_word`.
 - Real domain proposal prompts for production modules.
 - End-to-end transcript polishing with real module behavior.
 
@@ -43,7 +45,8 @@ Phase sequencing note:
 - Phase 9 LLM infrastructure is complete (structured client, scheduler, effective config resolution, diagnostics primitives);
 - Phase 10 LLM-backed validator runtime integration is complete;
 - Phase 11 shared proposal-generation framework and module-registry scaffolding are complete;
-- next recommended phase is Phase 12 (grammar module).
+- Phase 12 grammar module implementation and explicit runtime wiring are complete;
+- next recommended phase is Phase 13 (glossary module and protected-term behavior).
 
 ## Actual Go package layout
 
@@ -102,6 +105,10 @@ internal/framework/proposal_generation/
 internal/framework/modules/
   registry.go
 
+internal/modules/grammar/
+  module.go
+  prompt.go
+
 internal/framework/validators/
   models.go
   deterministic.go
@@ -136,16 +143,19 @@ Current runtime flow (`internal/cli/run.go`):
 9. Write normalized transcript and normalization summary artifacts.
 10. Chunk normalized transcript and compute chunk summaries.
 11. Write chunking summary artifact.
-12. Optionally execute runner modules sequentially when a module factory is injected (tests currently use this path; production defaults still avoid real module execution).
+12. Execute runner modules sequentially when:
+    - `--modules` is explicitly provided (production grammar path); or
+    - a test/injected module factory is provided.
 13. Output working transcript to `--output` file or stdout.
-14. Build process report (`phase` currently set to `phase11-proposal-generation-framework`).
+14. Build process report (`phase` currently set to `phase12-grammar-module`).
 15. Optionally write `--report-json`; always write run-dir `report.json`.
 16. Apply work-dir retention.
 
 Important behavior details:
 - Glossary is validated but not yet used for real correction module logic.
-- Default production CLI behavior remains deterministic normalization/chunking output because no real module implementations are registered yet.
-- No real LLM calls occur in the default production runtime path because no real modules are registered yet.
+- Default production CLI behavior remains deterministic normalization/chunking/reporting unless modules are explicitly selected with `--modules`.
+- Explicit `--modules grammar` runs the production grammar module path with LLM-backed proposal generation and validator-chain execution.
+- Default runs (without explicit module selection) do not perform LLM calls.
 - Success path is generally quiet on stderr.
 - Source IDs are preserved into a canonical transcript before normalization; normalization then reassigns output IDs sequentially from `1`.
 
@@ -193,7 +203,7 @@ Implemented config surfaces include:
 - work-dir and retention mode
 
 Current caveat:
-- LLM/module-related settings are mostly infrastructure-only today; default runtime path does not execute real modules.
+- LLM/module-related settings are active for explicit grammar runs; the default non-explicit path remains deterministic.
 
 ## Implemented structured LLM infrastructure
 `internal/framework/contracts` now defines a typed structured-completion contract:
@@ -209,8 +219,8 @@ Current caveat:
 - API-key redaction in adapter-returned errors.
 
 Current runtime boundary:
-- the default CLI runtime path still does not instantiate real production modules, so no default end-to-end LLM polishing occurs.
-- LLM calls are exercised only when test/injected modules and validators are provided.
+- the default CLI runtime path (without explicit module selection) still does not instantiate the full production module sequence.
+- LLM calls are exercised in production when `--modules grammar` is explicitly requested and in tests when fake/injected clients are used.
 
 `internal/framework/llm` also provides:
 - a bounded `Scheduler` for controlled concurrent LLM calls with reliable permit release;
@@ -252,7 +262,7 @@ Current behavior details:
 
 `internal/framework/contracts` provides interfaces and run-spec metadata scaffolding, including deterministic repeated module instance naming (`ResolveModuleRunSpecs`).
 
-These primitives are wired into the production runner and report model. Real module implementations are still pending.
+These primitives are wired into the production runner and report model. The grammar module is implemented; other production modules remain pending.
 
 ## Implemented validator runtime infrastructure
 `internal/framework/validators` provides deterministic validator infrastructure:
@@ -317,7 +327,18 @@ This helper only produces candidate proposals; validator-chain execution and pro
   - diagnostics directory context
 - returns explicit errors for unknown keys (`unsupported_module`) and recognized-but-unimplemented keys (`unimplemented_module`).
 
-No real production correction modules are registered yet.
+The `grammar` module key is now registered and constructible. `glossary`, `homophones`, and `spoken_word` remain recognized-but-unimplemented.
+
+## Implemented grammar production module
+`internal/modules/grammar` now provides the first production module:
+- prompt builder faithfully constrained to punctuation/capitalization/spacing/article cleanup;
+- explicit guardrails against meaning-changing rewrites, style rewrites, summarization, and invention;
+- proposal generation through `internal/framework/proposal_generation` and `contracts.StructuredLLMClient`;
+- scheduler-aware proposal calls through existing `contracts.LLMScheduler` hooks;
+- replacement policy `require_unique` (matching Python implementation);
+- validator chain integration using existing deterministic + LLM-backed validators;
+- grammar confidence threshold enforcement through existing validator/config infrastructure;
+- module-level reporting and diagnostics capture through existing runner/reporting paths.
 
 ## Reports and diagnostics (implemented)
 Current per-run artifacts include:
@@ -357,7 +378,8 @@ Retention modes implemented in `ApplyRetention`:
 - failed runs are always retained.
 
 Current runtime note:
-- real module execution is not implemented yet, so normal successful runs generally have no skipped corrections and `auto` typically removes clean successful run directories.
+- default non-explicit runs usually have no module-level skipped corrections, so `auto` commonly removes clean successful run directories.
+- explicit grammar runs can produce validator rejections and application skips, which are reflected in reports and retention input.
 
 Intentionally deferred to module/LLM phases:
 - real domain proposal prompts and production module implementations remain tied to later module phases.
@@ -378,8 +400,9 @@ Implemented tests currently cover:
 - LLM-backed validator batching, prompt builders, structured-response safety, scheduler hooks, and diagnostics redaction (`internal/framework/validators/*_test.go`, `internal/framework/runner/*_test.go`)
 - shared proposal-generation request/response parsing, deterministic indexing, scheduler hooks, and diagnostics redaction (`internal/framework/proposal_generation/*_test.go`, `internal/framework/runner/*_test.go`)
 - production module-registry known-key recognition and unsupported/unimplemented error behavior (`internal/framework/modules/*_test.go`, `internal/cli/run_test.go`)
+- production grammar module prompt constraints, proposal mapping, validator-chain behavior, confidence-threshold enforcement, diagnostics redaction, and explicit CLI/runtime integration (`internal/modules/grammar/*_test.go`, `internal/cli/run_test.go`, `internal/framework/runner/*_test.go`)
 
-Not covered yet (because not implemented): real production module implementations and full transcript-polishing runtime behavior.
+Not covered yet (because not implemented): production `glossary`, `homophones`, and `spoken_word` modules plus full default-sequence transcript-polishing runtime behavior.
 
 ## Intended final architecture (not yet implemented)
 The intended end-state still matches the rewrite plan:
diff --git a/docs/rewrite-notes.md b/docs/rewrite-notes.md
index b8f09cf..b3c2047 100644
--- a/docs/rewrite-notes.md
+++ b/docs/rewrite-notes.md
@@ -59,6 +59,8 @@ Implemented:
 - Deterministic proposal-index assignment for shared proposal generation.
 - Proposal-generation prompt/response diagnostics artifact wiring with secret redaction.
 - Production module-registry scaffolding with known key recognition and explicit unsupported/unimplemented errors.
+- Production grammar module package with Python-aligned prompt intent and guardrails.
+- Explicit `--modules grammar` runtime path through runner, shared proposal generation, validators, application, reporting, and diagnostics.
 - Broad deterministic and CLI/subprocess test coverage for implemented phases through `go test ./...`.
 - Internal typed structured LLM contract (`StructuredLLMClient.CompleteStructured(ctx, req, out)`).
 - `internal/framework/llm` instructor-go-backed adapter with:
@@ -74,8 +76,8 @@ Implemented:
 - Generic JSON diagnostics primitives for LLM interactions (request metadata, request payload, response payload, optional error payload) with secret redaction.
 
 Not yet implemented in runtime pipeline:
-- Real correction modules.
-- Domain proposal prompts for real modules.
+- Real correction modules for `glossary`, `homophones`, and `spoken_word`.
+- Domain proposal prompts for remaining real modules.
 - End-to-end transcript polishing behavior.
 
 ## Completed phases
@@ -214,7 +216,7 @@ Not implemented in Phase 8 (by design):
 
 ## Remaining work plan
 
-Next recommended phase: **Phase 12 (grammar module)**.
+Next recommended phase: **Phase 13 (glossary module and protected-term behavior)**.
 
 ## Phase 9: Structured LLM client and scheduler infrastructure
 
@@ -333,52 +335,30 @@ Implemented:
 - Runner/CLI injection-path tests showing shared proposal generation can flow through runner validation/application semantics using fake modules/clients.
 
 Not implemented in Phase 11 (by design):
-- Real production `glossary`, `homophones`, `spoken_word`, and `grammar` modules.
+- Real production `glossary`, `homophones`, and `spoken_word` modules.
 - Domain proposal prompts for production modules.
 - Default CLI end-to-end transcript polishing behavior.
 
 ## Phase 12: Grammar module
 
-### Purpose
+Completed.
 
-Implement the first production module in the Go runtime path. Grammar is a good first real module because it exercises LLM proposal generation and validator chains while remaining constrained to punctuation, capitalization, and spacing cleanup.
+Implemented:
+- Production grammar module package in `internal/modules/grammar`.
+- Grammar prompt builder aligned to Python intent and constrained to punctuation/capitalization/spacing/article cleanup.
+- Grammar proposal generation through shared `internal/framework/proposal_generation` using `contracts.StructuredLLMClient`.
+- Scheduler-aware grammar proposal generation through existing scheduler hooks.
+- Grammar replacement policy `require_unique` (matching Python behavior).
+- Grammar validator chain using existing deterministic and LLM-backed validator infrastructure.
+- Grammar confidence threshold enforcement through existing config + confidence-threshold validator behavior.
+- Explicit runtime support for `--modules grammar` through normalization, chunking, runner, proposal generation, validation, application, and reporting.
+- Prompt/response diagnostics artifacts for grammar proposal + validator interactions with secret redaction.
+- Module-level reports for grammar including validator decisions/rejections, applied changes, and skipped changes.
+- CLI/runtime fake-client tests for approved proposals, validator rejection, application skips, diagnostics, failure/error.log behavior, and report outputs (`--report-json` and run-dir `report.json`).
 
-### Scope
-
-Implement:
-- `grammar` module package.
-- Grammar prompt builder ported from the Python implementation.
-- Grammar structured response model.
-- Grammar replacement policy.
-- Grammar validator chain.
-- Grammar confidence threshold handling.
-- Prompt/response diagnostics.
-- Module-level report integration.
-- CLI support for `--modules grammar`.
-- Fake LLM tests.
-- Optional real LLM smoke test gated so normal `go test ./...` does not require credentials.
-
-Do not implement:
-- Glossary module.
-- Homophones module.
-- Spoken-word module.
-- Default full module sequence as active parity claim.
-
-### Expected behavior at end of phase
-
-Running `audita process ... --modules grammar` should perform real grammar-stage transcript polishing using the configured LLM endpoint.
-
-### Definition of done
-
-- Grammar module runs in the production runner.
-- Grammar module generates structured proposals through the LLM client.
-- Grammar validator chain runs.
-- Approved grammar proposals are applied.
-- Applied/skipped grammar changes appear in reports.
-- Prompt/response diagnostics are written.
-- `--modules grammar` works end-to-end.
-- Default pipeline is not yet claimed complete.
-- `go test ./...` passes without requiring external LLM credentials.
+Not implemented in Phase 12 (by design):
+- Production `glossary`, `homophones`, and `spoken_word` modules.
+- Full default module sequence execution as a feature-complete claim.
 
 ## Phase 13: Glossary module and protected-term behavior
 
diff --git a/internal/cli/run.go b/internal/cli/run.go
index 1bea029..cc38fdd 100644
--- a/internal/cli/run.go
+++ b/internal/cli/run.go
@@ -18,15 +18,18 @@ import (
 	"gitea.maximumdirect.net/eric/audita/internal/core/reporting"
 	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/llm"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/modules"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/runner"
 )
 
 type processInvocation struct {
-	TranscriptPath string
-	GlossaryPath   string
-	OutputPath     string
-	ReportJSONPath string
-	Config         config.Config
+	TranscriptPath  string
+	GlossaryPath    string
+	OutputPath      string
+	ReportJSONPath  string
+	Config          config.Config
+	ExplicitModules bool
 }
 
 var processModuleFactory runner.ModuleFactory
@@ -127,22 +130,71 @@ var processRunner = func(inv processInvocation, stdout io.Writer) (*normalizatio
 
 	workingTranscript := normalizedTranscript
 	var runOutput *runner.RunOutput
-	if processModuleFactory != nil {
+	moduleFactory := processModuleFactory
+	if moduleFactory == nil && inv.ExplicitModules {
+		moduleFactory = modules.NewFactory(modules.Dependencies{
+			Config:         &inv.Config,
+			Glossary:       glossary,
+			DiagnosticsDir: runDir.Path(),
+		})
+	}
+	if moduleFactory != nil {
+		proposalLLMClient := processProposalLLMClient
+		validationLLMClient := processValidationLLMClient
+		proposalScheduler := processProposalLLMScheduler
+		validationScheduler := processValidationLLMScheduler
+
+		if processModuleFactory == nil {
+			// Production runtime path: construct clients/schedulers from config.
+			if proposalLLMClient == nil {
+				primaryCfg := llm.ResolvePrimaryConfig(inv.Config)
+				client, clientErr := llm.NewInstructorClient(primaryCfg.ToInstructorClientConfig(llm.ModeJSON, nil))
+				if clientErr != nil {
+					return fail("runner_setup", clientErr, nil)
+				}
+				proposalLLMClient = client
+			}
+			if validationLLMClient == nil {
+				validationCfg := llm.ResolveValidationConfig(inv.Config)
+				client, clientErr := llm.NewInstructorClient(validationCfg.ToInstructorClientConfig(llm.ModeJSON, nil))
+				if clientErr != nil {
+					return fail("runner_setup", clientErr, nil)
+				}
+				validationLLMClient = client
+			}
+			if proposalScheduler == nil {
+				primaryCfg := llm.ResolvePrimaryConfig(inv.Config)
+				s, sErr := llm.NewScheduler(primaryCfg.Concurrency)
+				if sErr != nil {
+					return fail("runner_setup", sErr, nil)
+				}
+				proposalScheduler = s
+			}
+			if validationScheduler == nil {
+				validationCfg := llm.ResolveValidationConfig(inv.Config)
+				s, sErr := llm.NewScheduler(validationCfg.Concurrency)
+				if sErr != nil {
+					return fail("runner_setup", sErr, nil)
+				}
+				validationScheduler = s
+			}
+		}
+
 		moduleSpecs, err := contracts.ResolveModuleRunSpecs(inv.Config.Modules)
 		if err != nil {
 			return fail("runner_setup", err, nil)
 		}
 
-		runnerResult, runErr := runner.New(processModuleFactory).Run(context.Background(), runner.RunInput{
+		runnerResult, runErr := runner.New(moduleFactory).Run(context.Background(), runner.RunInput{
 			Config:                   &inv.Config,
 			Transcript:               normalizedTranscript,
 			Glossary:                 glossary,
 			ModuleSpecs:              moduleSpecs,
-			ProposalLLMClient:        processProposalLLMClient,
-			ProposalLLMScheduler:     processProposalLLMScheduler,
+			ProposalLLMClient:        proposalLLMClient,
+			ProposalLLMScheduler:     proposalScheduler,
 			ProposalDiagnosticsDir:   runDir.Path(),
-			ValidationLLMClient:      processValidationLLMClient,
-			ValidationLLMScheduler:   processValidationLLMScheduler,
+			ValidationLLMClient:      validationLLMClient,
+			ValidationLLMScheduler:   validationScheduler,
 			ValidationDiagnosticsDir: runDir.Path(),
 		})
 		runOutput = &runnerResult
@@ -243,9 +295,11 @@ func runProcess(args []string, stdout, stderr io.Writer) int {
 	}
 
 	overrides := config.CLIOverrides{}
+	explicitModules := false
 	fs.Visit(func(f *flag.Flag) {
 		switch f.Name {
 		case "modules":
+			explicitModules = true
 			overrides.ModulesCSV = pFlags.modules
 		case "llm-api-key":
 			overrides.PrimaryLLMAPIKey = pFlags.llmAPIKey
@@ -322,11 +376,12 @@ func runProcess(args []string, stdout, stderr io.Writer) int {
 	}
 
 	inv := processInvocation{
-		TranscriptPath: positional[0],
-		GlossaryPath:   *pFlags.glossaryPath,
-		OutputPath:     *pFlags.outputPath,
-		ReportJSONPath: *pFlags.reportJSONPath,
-		Config:         cfg,
+		TranscriptPath:  positional[0],
+		GlossaryPath:    *pFlags.glossaryPath,
+		OutputPath:      *pFlags.outputPath,
+		ReportJSONPath:  *pFlags.reportJSONPath,
+		Config:          cfg,
+		ExplicitModules: explicitModules,
 	}
 
 	normSummary, chunkSummary, runOutput, runDir, runErr := processRunner(inv, stdout)
@@ -405,7 +460,7 @@ func extractErrorPhase(err error) (phase string, message string) {
 
 func buildProcessReport(status string, inv processInvocation, runDir *diagnostics.RunDirectory, startedAt, completedAt time.Time, errorMessage string, errorPhase string, normalizationSummary *normalization.NormalizationSummary, chunkingSummary *chunking.Summary, runOutput *runner.RunOutput) reporting.ProcessReport {
 	report := reporting.ProcessReport{
-		Phase:          "phase11-proposal-generation-framework",
+		Phase:          "phase12-grammar-module",
 		Status:         status,
 		Operation:      "process",
 		TranscriptPath: inv.TranscriptPath,
diff --git a/internal/cli/run_test.go b/internal/cli/run_test.go
index 7ca607e..3aa54f3 100644
--- a/internal/cli/run_test.go
+++ b/internal/cli/run_test.go
@@ -15,6 +15,7 @@ import (
 	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/modules"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/proposal_generation"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/proposals"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/validators"
 )
@@ -615,8 +616,8 @@ func TestRunProcessReportJSONIncludesChunkingSummary(t *testing.T) {
 	if report.Chunking.MaxSectionTokens == 0 {
 		t.Errorf("expected max_section_tokens in report")
 	}
-	if report.Phase != "phase11-proposal-generation-framework" {
-		t.Errorf("expected phase 'phase11-proposal-generation-framework', got %q", report.Phase)
+	if report.Phase != "phase12-grammar-module" {
+		t.Errorf("expected phase 'phase12-grammar-module', got %q", report.Phase)
 	}
 }
 
@@ -661,8 +662,9 @@ func (v fakeValidator) Validate(ctx context.Context, req contracts.ValidationReq
 }
 
 type fakeStructuredLLMClient struct {
-	responses []validators.LLMValidationResponse
-	err       error
+	validationResponses []validators.LLMValidationResponse
+	proposalResponses   []proposal_generation.StructuredCorrectionSet
+	err                 error
 }
 
 func (f *fakeStructuredLLMClient) CompleteStructured(ctx context.Context, req contracts.StructuredCompletionRequest, out any) (contracts.StructuredCompletionResponse, error) {
@@ -671,13 +673,24 @@ func (f *fakeStructuredLLMClient) CompleteStructured(ctx context.Context, req co
 	if f.err != nil {
 		return contracts.StructuredCompletionResponse{}, f.err
 	}
-	if len(f.responses) == 0 {
-		return contracts.StructuredCompletionResponse{}, errors.New("unexpected llm call")
+	switch target := out.(type) {
+	case *validators.LLMValidationResponse:
+		if len(f.validationResponses) == 0 {
+			return contracts.StructuredCompletionResponse{}, errors.New("unexpected validation llm call")
+		}
+		*target = f.validationResponses[0]
+		f.validationResponses = f.validationResponses[1:]
+		return contracts.StructuredCompletionResponse{}, nil
+	case *proposal_generation.StructuredCorrectionSet:
+		if len(f.proposalResponses) == 0 {
+			return contracts.StructuredCompletionResponse{}, errors.New("unexpected proposal llm call")
+		}
+		*target = f.proposalResponses[0]
+		f.proposalResponses = f.proposalResponses[1:]
+		return contracts.StructuredCompletionResponse{}, nil
+	default:
+		return contracts.StructuredCompletionResponse{}, errors.New("unexpected llm output type")
 	}
-	target := out.(*validators.LLMValidationResponse)
-	*target = f.responses[0]
-	f.responses = f.responses[1:]
-	return contracts.StructuredCompletionResponse{}, nil
 }
 
 func TestRunProcessInjectedFactoryExecutesRunnerAndReportsModules(t *testing.T) {
@@ -771,7 +784,7 @@ func TestRunProcessInjectedFactoryLLMValidatorResultsInReports(t *testing.T) {
 		t.Fatalf("NewLLMBackedValidator: %v", err)
 	}
 	processValidationLLMClient = &fakeStructuredLLMClient{
-		responses: []validators.LLMValidationResponse{{
+		validationResponses: []validators.LLMValidationResponse{{
 			Validations: []validators.LLMValidationDecision{{CorrectionIndex: 0, Approved: false, Confidence: 0.99, Reason: "reject"}},
 		}},
 	}
@@ -940,6 +953,249 @@ func TestRunProcessProductionRegistryUnimplementedModuleFailsCleanly(t *testing.
 	}
 }
 
+func TestRunProcessExplicitUnimplementedModulesFailClearly(t *testing.T) {
+	for _, moduleKey := range []string{"glossary", "homophones", "spoken_word"} {
+		t.Run(moduleKey, func(t *testing.T) {
+			var stdout, stderr bytes.Buffer
+			transcriptPath := writeFile(t, "transcript.json", `[
+  {"id":1,"speaker":"Alice","start":0.0,"end":1.0,"text":"Hello"}
+]`)
+			exitCode := Run([]string{
+				"process", transcriptPath,
+				"--glossary", fixturePath("tiny_glossary.yaml"),
+				"--modules", moduleKey,
+			}, &stdout, &stderr)
+			if exitCode == 0 {
+				t.Fatalf("expected failure for %s", moduleKey)
+			}
+			if stdout.Len() != 0 {
+				t.Fatalf("expected empty stdout on failure, got %q", stdout.String())
+			}
+			if !strings.Contains(stderr.String(), "recognized but not implemented") {
+				t.Fatalf("expected unimplemented message, got %q", stderr.String())
+			}
+		})
+	}
+}
+
+func TestRunProcessExplicitGrammarAppliesCorrectionAndReportsDiagnostics(t *testing.T) {
+	secret := "phase12-secret"
+	processProposalLLMClient = &fakeStructuredLLMClient{
+		proposalResponses: []proposal_generation.StructuredCorrectionSet{
+			{
+				Corrections: []proposal_generation.StructuredCorrectionProposal{
+					{TargetSegmentID: 1, OriginalText: "hello ,world", CorrectedText: "Hello, world", Confidence: 0.95},
+				},
+			},
+		},
+	}
+	processValidationLLMClient = &fakeStructuredLLMClient{
+		validationResponses: []validators.LLMValidationResponse{
+			{Validations: []validators.LLMValidationDecision{{CorrectionIndex: 0, Approved: true, Confidence: 0.99, Reason: "ok"}}},
+			{Validations: []validators.LLMValidationDecision{{CorrectionIndex: 0, Approved: true, Confidence: 0.99, Reason: secret}}},
+		},
+	}
+	t.Setenv("AUDITA_LLM_API_KEY", secret)
+	t.Setenv("AUDITA_VALIDATION_LLM_API_KEY", secret)
+	t.Cleanup(func() {
+		processProposalLLMClient = nil
+		processValidationLLMClient = nil
+		processProposalLLMScheduler = nil
+		processValidationLLMScheduler = nil
+	})
+
+	var stdout, stderr bytes.Buffer
+	workDir := t.TempDir()
+	reportPath := filepath.Join(t.TempDir(), "report.json")
+	outputPath := filepath.Join(t.TempDir(), "out.json")
+	transcriptPath := writeFile(t, "transcript.json", `[
+  {"id":1,"speaker":"Alice","start":0.0,"end":1.0,"text":"hello ,world"}
+]`)
+
+	exitCode := Run([]string{
+		"process", transcriptPath,
+		"--glossary", fixturePath("tiny_glossary.yaml"),
+		"--modules", "grammar",
+		"--output", outputPath,
+		"--report-json", reportPath,
+		"--work-dir", workDir,
+		"--work-dir-retention", "always",
+	}, &stdout, &stderr)
+	if exitCode != 0 {
+		t.Fatalf("expected success, got %d stderr=%q", exitCode, stderr.String())
+	}
+	if stdout.Len() != 0 {
+		t.Fatalf("expected empty stdout with --output, got %q", stdout.String())
+	}
+
+	parsed, err := schema.ParseTranscriptJSON(readFile(t, outputPath))
+	if err != nil {
+		t.Fatalf("parse output: %v", err)
+	}
+	if parsed.Segments[0].Text != "Hello, world" {
+		t.Fatalf("expected grammar correction applied, got %q", parsed.Segments[0].Text)
+	}
+
+	report := readProcessReport(t, reportPath)
+	if len(report.ModuleResults) != 1 || report.ModuleResults[0].ModuleKey != "grammar" {
+		t.Fatalf("expected one grammar module result, got %+v", report.ModuleResults)
+	}
+	if len(report.ModuleResults[0].AppliedChanges) != 1 {
+		t.Fatalf("expected one applied grammar change, got %+v", report.ModuleResults[0].AppliedChanges)
+	}
+	if len(report.ModuleResults[0].ValidatorDecisions) == 0 {
+		t.Fatalf("expected validator decisions in report")
+	}
+
+	runDir := onlyRunDir(t, workDir)
+	runReport := readProcessReport(t, filepath.Join(runDir, "report.json"))
+	if len(runReport.ModuleResults) != 1 {
+		t.Fatalf("expected module results in run-dir report")
+	}
+
+	diagFiles, globErr := filepath.Glob(filepath.Join(runDir, "grammar", "*response-payload.json"))
+	if globErr != nil {
+		t.Fatalf("glob diagnostics: %v", globErr)
+	}
+	if len(diagFiles) == 0 {
+		t.Fatalf("expected grammar diagnostics payload files in %s", filepath.Join(runDir, "grammar"))
+	}
+	for _, f := range diagFiles {
+		raw := string(readFile(t, f))
+		if strings.Contains(raw, secret) {
+			t.Fatalf("secret leaked in diagnostics %q: %s", f, raw)
+		}
+	}
+}
+
+func TestRunProcessExplicitGrammarRejectedAndApplicationSkipAreDistinct(t *testing.T) {
+	processProposalLLMClient = &fakeStructuredLLMClient{
+		proposalResponses: []proposal_generation.StructuredCorrectionSet{
+			{
+				Corrections: []proposal_generation.StructuredCorrectionProposal{
+					{TargetSegmentID: 1, OriginalText: "Hello", CorrectedText: "Hi", Confidence: 0.99},
+					{TargetSegmentID: 1, OriginalText: "Hello world", CorrectedText: "Hi world", Confidence: 0.99},
+					{TargetSegmentID: 1, OriginalText: "world", CorrectedText: "earth", Confidence: 0.99},
+				},
+			},
+		},
+	}
+	processValidationLLMClient = &fakeStructuredLLMClient{
+		validationResponses: []validators.LLMValidationResponse{
+			{
+				Validations: []validators.LLMValidationDecision{
+					{CorrectionIndex: 0, Approved: true, Confidence: 0.9, Reason: "ok"},
+					{CorrectionIndex: 1, Approved: true, Confidence: 0.9, Reason: "ok"},
+					{CorrectionIndex: 2, Approved: false, Confidence: 0.9, Reason: "reject"},
+				},
+			},
+			{
+				Validations: []validators.LLMValidationDecision{
+					{CorrectionIndex: 0, Approved: true, Confidence: 0.9, Reason: "ok"},
+					{CorrectionIndex: 1, Approved: true, Confidence: 0.9, Reason: "ok"},
+				},
+			},
+		},
+	}
+	t.Cleanup(func() {
+		processProposalLLMClient = nil
+		processValidationLLMClient = nil
+	})
+
+	var stdout, stderr bytes.Buffer
+	reportPath := filepath.Join(t.TempDir(), "report.json")
+	outputPath := filepath.Join(t.TempDir(), "out.json")
+	transcriptPath := writeFile(t, "transcript.json", `[
+  {"id":1,"speaker":"Alice","start":0.0,"end":1.0,"text":"Hello world"}
+]`)
+	exitCode := Run([]string{
+		"process", transcriptPath,
+		"--glossary", fixturePath("tiny_glossary.yaml"),
+		"--modules", "grammar",
+		"--output", outputPath,
+		"--report-json", reportPath,
+	}, &stdout, &stderr)
+	if exitCode != 0 {
+		t.Fatalf("expected success, got %d stderr=%q", exitCode, stderr.String())
+	}
+
+	report := readProcessReport(t, reportPath)
+	if len(report.ModuleResults) != 1 {
+		t.Fatalf("expected one module result")
+	}
+	module := report.ModuleResults[0]
+	if len(module.ValidatorRejected) != 1 {
+		t.Fatalf("expected one validator rejection, got %+v", module.ValidatorRejected)
+	}
+	if len(module.SkippedChanges) != 1 {
+		t.Fatalf("expected one application skip, got %+v", module.SkippedChanges)
+	}
+	if module.ValidatorRejected[0].ReasonCode == string(module.SkippedChanges[0].SkipReason) {
+		t.Fatalf("validator rejection and application skip should remain distinct")
+	}
+}
+
+func TestRunProcessExplicitGrammarMalformedLLMOutputFailsWithErrorLog(t *testing.T) {
+	processProposalLLMClient = &fakeStructuredLLMClient{err: errors.New("malformed structured output")}
+	t.Cleanup(func() { processProposalLLMClient = nil })
+
+	var stdout, stderr bytes.Buffer
+	workDir := t.TempDir()
+	reportPath := filepath.Join(t.TempDir(), "report.json")
+	transcriptPath := writeFile(t, "transcript.json", `[
+  {"id":1,"speaker":"Alice","start":0.0,"end":1.0,"text":"hello"}
+]`)
+
+	exitCode := Run([]string{
+		"process", transcriptPath,
+		"--glossary", fixturePath("tiny_glossary.yaml"),
+		"--modules", "grammar",
+		"--work-dir", workDir,
+		"--work-dir-retention", "always",
+		"--report-json", reportPath,
+	}, &stdout, &stderr)
+	if exitCode == 0 {
+		t.Fatal("expected failure")
+	}
+	if stdout.Len() != 0 {
+		t.Fatalf("expected empty stdout on failure, got %q", stdout.String())
+	}
+	if !strings.Contains(stderr.String(), "runner_execution") {
+		t.Fatalf("expected runner_execution error, got %q", stderr.String())
+	}
+	runDir := onlyRunDir(t, workDir)
+	if _, err := os.Stat(filepath.Join(runDir, "error.log")); err != nil {
+		t.Fatalf("expected error.log on failed grammar run: %v", err)
+	}
+	report := readProcessReport(t, reportPath)
+	if report.Status != "failed" || report.ErrorPhase != "runner_execution" {
+		t.Fatalf("expected failed runner_execution report, got %+v", report)
+	}
+}
+
+func TestRunProcessDefaultBehaviorRemainsDeterministicWithoutExplicitModules(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	reportPath := filepath.Join(t.TempDir(), "report.json")
+	outputPath := filepath.Join(t.TempDir(), "out.json")
+	transcriptPath := writeFile(t, "transcript.json", `[
+  {"id":1,"speaker":"Alice","start":0.0,"end":1.0,"text":"hello ,world"}
+]`)
+
+	exitCode := Run([]string{
+		"process", transcriptPath,
+		"--glossary", fixturePath("tiny_glossary.yaml"),
+		"--output", outputPath,
+		"--report-json", reportPath,
+	}, &stdout, &stderr)
+	if exitCode != 0 {
+		t.Fatalf("expected success, got %d stderr=%q", exitCode, stderr.String())
+	}
+	report := readProcessReport(t, reportPath)
+	if report.ModulesSummary != nil || len(report.ModuleResults) != 0 {
+		t.Fatalf("expected no module execution without explicit --modules, got summary=%+v results=%+v", report.ModulesSummary, report.ModuleResults)
+	}
+}
+
 func TestRunProcessChunkingSummaryArtifactWritten(t *testing.T) {
 	var stdout bytes.Buffer
 	var stderr bytes.Buffer
diff --git a/internal/core/reporting/report_test.go b/internal/core/reporting/report_test.go
index 83afcde..e53658b 100644
--- a/internal/core/reporting/report_test.go
+++ b/internal/core/reporting/report_test.go
@@ -11,7 +11,7 @@ import (
 func TestProcessReportModuleResultsJSONSuccessAndSkipped(t *testing.T) {
 	now := time.Now().UTC()
 	report := ProcessReport{
-		Phase:  "phase11-proposal-generation-framework",
+		Phase:  "phase12-grammar-module",
 		Status: "success",
 		ModuleResults: []ModuleReport{
 			{
@@ -80,7 +80,7 @@ func TestProcessReportModuleResultsJSONSuccessAndSkipped(t *testing.T) {
 func TestProcessReportModuleResultsJSONFailedModule(t *testing.T) {
 	now := time.Now().UTC()
 	report := ProcessReport{
-		Phase:  "phase11-proposal-generation-framework",
+		Phase:  "phase12-grammar-module",
 		Status: "failed",
 		ModuleResults: []ModuleReport{
 			{
diff --git a/internal/framework/modules/registry.go b/internal/framework/modules/registry.go
index e57424f..4a702d8 100644
--- a/internal/framework/modules/registry.go
+++ b/internal/framework/modules/registry.go
@@ -8,6 +8,7 @@ import (
 	"gitea.maximumdirect.net/eric/audita/internal/core/config"
 	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
+	grammarmodule "gitea.maximumdirect.net/eric/audita/internal/modules/grammar"
 )
 
 const (
@@ -65,10 +66,12 @@ type Factory struct {
 // NewFactory creates a production registry scaffold with known module keys but
 // no real module constructors registered yet.
 func NewFactory(deps Dependencies) *Factory {
-	return &Factory{
+	factory := &Factory{
 		deps:         deps,
 		constructors: make(map[string]Constructor, len(knownModuleKeys)),
 	}
+	_ = factory.RegisterConstructor(ModuleKeyGrammar, constructGrammarModule)
+	return factory
 }
 
 // RegisterConstructor registers a constructor for a known module key.
@@ -87,6 +90,12 @@ func (f *Factory) RegisterConstructor(moduleKey string, constructor Constructor)
 	return nil
 }
 
+func constructGrammarModule(ctx context.Context, req ConstructRequest) (contracts.TranscriptModule, error) {
+	_ = ctx
+	_ = req
+	return grammarmodule.New()
+}
+
 // ModuleForSpec resolves one configured run spec into a module instance.
 func (f *Factory) ModuleForSpec(spec contracts.ModuleRunSpec) (contracts.TranscriptModule, error) {
 	if f == nil {
diff --git a/internal/framework/modules/registry_test.go b/internal/framework/modules/registry_test.go
index 35392af..120bad0 100644
--- a/internal/framework/modules/registry_test.go
+++ b/internal/framework/modules/registry_test.go
@@ -66,7 +66,7 @@ func TestUnsupportedUnknownModuleKeyFailsCleanly(t *testing.T) {
 
 func TestRecognizedButUnimplementedModuleKeyFailsCleanly(t *testing.T) {
 	factory := NewFactory(Dependencies{})
-	for _, key := range []string{ModuleKeyGlossary, ModuleKeyHomophones, ModuleKeySpokenWord, ModuleKeyGrammar} {
+	for _, key := range []string{ModuleKeyGlossary, ModuleKeyHomophones, ModuleKeySpokenWord} {
 		t.Run(key, func(t *testing.T) {
 			_, err := factory.ModuleForSpec(contracts.ModuleRunSpec{ModuleKey: key, InstanceName: key})
 			if err == nil {
@@ -84,6 +84,17 @@ func TestRecognizedButUnimplementedModuleKeyFailsCleanly(t *testing.T) {
 	}
 }
 
+func TestGrammarIsRegisteredAndConstructibleByDefault(t *testing.T) {
+	factory := NewFactory(Dependencies{})
+	module, err := factory.ModuleForSpec(contracts.ModuleRunSpec{ModuleKey: ModuleKeyGrammar, InstanceName: ModuleKeyGrammar})
+	if err != nil {
+		t.Fatalf("ModuleForSpec error: %v", err)
+	}
+	if module.Key() != ModuleKeyGrammar {
+		t.Fatalf("expected grammar module key, got %q", module.Key())
+	}
+}
+
 func TestRegisterConstructorAndConstruct(t *testing.T) {
 	factory := NewFactory(Dependencies{})
 	if err := factory.RegisterConstructor(ModuleKeyGlossary, func(ctx context.Context, req ConstructRequest) (contracts.TranscriptModule, error) {
diff --git a/internal/framework/proposal_generation/generate.go b/internal/framework/proposal_generation/generate.go
index 320eab0..f85331c 100644
--- a/internal/framework/proposal_generation/generate.go
+++ b/internal/framework/proposal_generation/generate.go
@@ -54,6 +54,7 @@ type Request struct {
 	Config            *config.Config              `json:"-"`
 	Messages          []contracts.LLMMessage      `json:"messages"`
 	Model             string                      `json:"model,omitempty"`
+	StageName         string                      `json:"stage_name,omitempty"`
 	StartIndex        int                         `json:"start_index"`
 	LLMClient         contracts.StructuredLLMClient
 	Scheduler         contracts.LLMScheduler
@@ -87,7 +88,10 @@ func GenerateCandidates(ctx context.Context, req Request) (Result, error) {
 		return Result{}, fmt.Errorf("messages must not be empty")
 	}
 
-	stage := buildStageName(req.ModuleInstance, req.Section)
+	stage := strings.TrimSpace(req.StageName)
+	if stage == "" {
+		stage = buildStageName(req.ModuleInstance, req.Section)
+	}
 	model := resolveModel(req.Config, req.Model)
 	messages := append([]contracts.LLMMessage(nil), req.Messages...)
 
diff --git a/internal/framework/runner/runner_test.go b/internal/framework/runner/runner_test.go
index 432f982..d2e96f7 100644
--- a/internal/framework/runner/runner_test.go
+++ b/internal/framework/runner/runner_test.go
@@ -12,6 +12,7 @@ import (
 	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/llm"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/modules"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/proposal_generation"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/proposals"
 	"gitea.maximumdirect.net/eric/audita/internal/framework/validators"
@@ -651,3 +652,37 @@ func TestRunnerProposalGenerationHelperFlowsThroughPipeline(t *testing.T) {
 		t.Fatalf("expected proposal-generation diagnostics artifacts in %s", filepath.Join(diagDir, "m"))
 	}
 }
+
+func TestRunnerGrammarModuleUsesConfidenceThreshold(t *testing.T) {
+	client := &fakeProposalStructuredClient{
+		responses: []proposal_generation.StructuredCorrectionSet{
+			{
+				Corrections: []proposal_generation.StructuredCorrectionProposal{
+					{TargetSegmentID: 1, OriginalText: "hello ,world", CorrectedText: "Hello, world", Confidence: 0.5},
+				},
+			},
+		},
+	}
+	cfg := config.Default()
+	cfg.Thresholds.Grammar = 0.9
+	factory := modules.NewFactory(modules.Dependencies{})
+	out, err := New(factory).Run(context.Background(), RunInput{
+		Config:            &cfg,
+		Transcript:        &schema.Transcript{Segments: []schema.Segment{{ID: 1, Text: "hello ,world"}}},
+		Glossary:          &schema.Glossary{},
+		ModuleSpecs:       []contracts.ModuleRunSpec{{ModuleKey: "grammar", InstanceName: "grammar"}},
+		ProposalLLMClient: client,
+	})
+	if err != nil {
+		t.Fatalf("Run error: %v", err)
+	}
+	if out.FinalTranscript.Segments[0].Text != "hello ,world" {
+		t.Fatalf("expected no changes due to confidence threshold, got %q", out.FinalTranscript.Segments[0].Text)
+	}
+	if len(out.ModuleResults) != 1 || len(out.ModuleResults[0].ValidatorRejected) == 0 {
+		t.Fatalf("expected validator rejection, got %+v", out.ModuleResults)
+	}
+	if out.ModuleResults[0].ValidatorRejected[0].ReasonCode != validators.ReasonLowConfidence {
+		t.Fatalf("expected low confidence reason, got %+v", out.ModuleResults[0].ValidatorRejected[0])
+	}
+}
diff --git a/internal/modules/grammar/module.go b/internal/modules/grammar/module.go
new file mode 100644
index 0000000..35ca22f
--- /dev/null
+++ b/internal/modules/grammar/module.go
@@ -0,0 +1,76 @@
+package grammar
+
+import (
+	"context"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/proposal_generation"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/proposals"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/validators"
+)
+
+type Module struct {
+	validators []contracts.Validator
+}
+
+func New() (*Module, error) {
+	grammarOnlyGuard, err := validators.NewLLMBackedValidator("grammar_only_guard", validators.LLMValidatorTypeGrammarReview, "")
+	if err != nil {
+		return nil, err
+	}
+	meaningReversal, err := validators.NewLLMBackedValidator("meaning_reversal_review", validators.LLMValidatorTypeMeaningReversal, "")
+	if err != nil {
+		return nil, err
+	}
+
+	return &Module{
+		validators: []contracts.Validator{
+			validators.NoEffectValidator{},
+			validators.OriginalTextPresenceValidator{},
+			validators.ConfidenceThresholdValidator{},
+			validators.ProtectedGlossaryTermValidator{},
+			validators.NonEmptyCorrectionValidator{},
+			grammarOnlyGuard,
+			meaningReversal,
+		},
+	}, nil
+}
+
+func (m *Module) Key() string { return "grammar" }
+
+func (m *Module) ReplacementPolicy() proposals.ReplacementPolicy {
+	// Python grammar module uses require_unique for conservative single-span replacement.
+	return proposals.ReplacementPolicyRequireUnique
+}
+
+func (m *Module) Validators() []contracts.Validator {
+	return append([]contracts.Validator(nil), m.validators...)
+}
+
+func (m *Module) Propose(ctx context.Context, req contracts.ProposalRequest) ([]proposals.CorrectionProposal, error) {
+	messages, err := BuildProposalMessages(req.WorkingTranscript, req.Glossary)
+	if err != nil {
+		return nil, err
+	}
+
+	generated, err := proposal_generation.GenerateCandidates(ctx, proposal_generation.Request{
+		ModuleKey:         req.RunSpec.ModuleKey,
+		ModuleInstance:    req.RunSpec.InstanceName,
+		ReplacementPolicy: req.RunSpec.ReplacementPolicy,
+		WorkingTranscript: req.WorkingTranscript,
+		Section:           req.Section,
+		Glossary:          req.Glossary,
+		Config:            req.Config,
+		Messages:          messages,
+		StageName:         fmt.Sprintf("%s:proposal", req.RunSpec.InstanceName),
+		StartIndex:        0,
+		LLMClient:         req.LLMClient,
+		Scheduler:         req.LLMScheduler,
+		DiagnosticsDir:    req.DiagnosticsDir,
+	})
+	if err != nil {
+		return nil, err
+	}
+	return generated.Corrections, nil
+}
diff --git a/internal/modules/grammar/module_test.go b/internal/modules/grammar/module_test.go
new file mode 100644
index 0000000..f242908
--- /dev/null
+++ b/internal/modules/grammar/module_test.go
@@ -0,0 +1,194 @@
+package grammar
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/audita/internal/core/config"
+	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/proposal_generation"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/proposals"
+)
+
+type fakeLLMClient struct {
+	responses []map[string]any
+	err       error
+	calls     []contracts.StructuredCompletionRequest
+}
+
+func (f *fakeLLMClient) CompleteStructured(ctx context.Context, req contracts.StructuredCompletionRequest, out any) (contracts.StructuredCompletionResponse, error) {
+	_ = ctx
+	f.calls = append(f.calls, req)
+	if f.err != nil {
+		return contracts.StructuredCompletionResponse{}, f.err
+	}
+	if len(f.responses) == 0 {
+		return contracts.StructuredCompletionResponse{}, errors.New("unexpected call")
+	}
+	payload := f.responses[0]
+	f.responses = f.responses[1:]
+
+	target, ok := out.(*proposal_generation.StructuredCorrectionSet)
+	if !ok {
+		return contracts.StructuredCompletionResponse{}, errors.New("unexpected output type")
+	}
+	items, _ := payload["corrections"].([]map[string]any)
+	for _, item := range items {
+		target.Corrections = append(target.Corrections, proposal_generation.StructuredCorrectionProposal{
+			TargetSegmentID: item["id"].(int),
+			OriginalText:    item["original_text"].(string),
+			CorrectedText:   item["corrected_text"].(string),
+			Confidence:      item["confidence"].(float64),
+		})
+	}
+	return contracts.StructuredCompletionResponse{}, nil
+}
+
+type countingScheduler struct {
+	runs int
+}
+
+func (s *countingScheduler) Run(ctx context.Context, fn func(context.Context) error) error {
+	s.runs++
+	return fn(ctx)
+}
+
+func tinyTranscript() *schema.Transcript {
+	return &schema.Transcript{Segments: []schema.Segment{
+		{ID: 1, Speaker: "A", Start: 0, End: 1, Text: "hello ,world"},
+	}}
+}
+
+func tinyGlossary() *schema.Glossary {
+	return &schema.Glossary{Entries: []schema.GlossaryEntry{
+		{Name: "Jesters", Category: "faction", Summary: "Faction", Aliases: []string{"Jester"}},
+	}}
+}
+
+func TestBuildProposalMessagesConstraints(t *testing.T) {
+	msgs, err := BuildProposalMessages(tinyTranscript(), tinyGlossary())
+	if err != nil {
+		t.Fatalf("BuildProposalMessages error: %v", err)
+	}
+	if len(msgs) != 2 {
+		t.Fatalf("expected 2 messages, got %d", len(msgs))
+	}
+	combined := msgs[0].Content + "\n" + msgs[1].Content
+	for _, want := range []string{
+		"Transcript section:",
+		"Protected glossary/context:",
+		"punctuation, capitalization, spacing, and article cleanup only",
+		"Do not make word substitutions",
+		"Do not return speaker, start, or end fields",
+		`"id": 1`,
+	} {
+		if !strings.Contains(combined, want) {
+			t.Fatalf("expected prompt to contain %q", want)
+		}
+	}
+	if strings.Contains(strings.ToLower(combined), "summarize") {
+		t.Fatalf("prompt should not invite summarization")
+	}
+}
+
+func TestGrammarModuleReplacementPolicy(t *testing.T) {
+	m, err := New()
+	if err != nil {
+		t.Fatalf("New error: %v", err)
+	}
+	if m.ReplacementPolicy() != proposals.ReplacementPolicyRequireUnique {
+		t.Fatalf("unexpected replacement policy: %q", m.ReplacementPolicy())
+	}
+}
+
+func TestGrammarModuleValidatorChain(t *testing.T) {
+	m, err := New()
+	if err != nil {
+		t.Fatalf("New error: %v", err)
+	}
+	got := make([]string, 0, len(m.Validators()))
+	for _, v := range m.Validators() {
+		got = append(got, v.Name())
+	}
+	want := []string{
+		"no_effect",
+		"original_text_presence",
+		"confidence_threshold",
+		"protected_glossary_terms",
+		"non_empty_correction",
+		"grammar_only_guard",
+		"meaning_reversal_review",
+	}
+	if strings.Join(got, ",") != strings.Join(want, ",") {
+		t.Fatalf("unexpected validator chain\n got: %v\nwant: %v", got, want)
+	}
+}
+
+func TestGrammarModuleProposeMapsCorrectionsAndWritesDiagnostics(t *testing.T) {
+	secret := "super-secret-key"
+	client := &fakeLLMClient{
+		responses: []map[string]any{
+			{
+				"corrections": []map[string]any{
+					{"id": 1, "original_text": "hello ,world", "corrected_text": "Hello, world", "confidence": 0.93},
+				},
+			},
+		},
+	}
+	scheduler := &countingScheduler{}
+	cfg := config.Default()
+	cfg.PrimaryLLM.APIKey = secret
+	module, err := New()
+	if err != nil {
+		t.Fatalf("New error: %v", err)
+	}
+	diagDir := t.TempDir()
+	out, err := module.Propose(context.Background(), contracts.ProposalRequest{
+		ExecutionContext: contracts.ExecutionContext{
+			Config:            &cfg,
+			WorkingTranscript: tinyTranscript(),
+			Glossary:          tinyGlossary(),
+			DiagnosticsDir:    diagDir,
+		},
+		RunSpec: contracts.ModuleRunSpec{
+			ModuleKey:         "grammar",
+			InstanceName:      "grammar",
+			ReplacementPolicy: proposals.ReplacementPolicyRequireUnique,
+		},
+		LLMClient:    client,
+		LLMScheduler: scheduler,
+	})
+	if err != nil {
+		t.Fatalf("Propose error: %v", err)
+	}
+	if scheduler.runs != 1 {
+		t.Fatalf("expected scheduler run count 1, got %d", scheduler.runs)
+	}
+	if len(client.calls) != 1 || client.calls[0].StageName != "grammar:proposal" {
+		t.Fatalf("expected one grammar:proposal call, got %+v", client.calls)
+	}
+	if len(out) != 1 || out[0].CorrectedText != "Hello, world" {
+		t.Fatalf("unexpected proposals: %+v", out)
+	}
+	diagFiles, globErr := filepath.Glob(filepath.Join(diagDir, "grammar", "*proposal*response-payload.json"))
+	if globErr != nil {
+		t.Fatalf("glob error: %v", globErr)
+	}
+	if len(diagFiles) == 0 {
+		t.Fatalf("expected diagnostics response payload under %s", filepath.Join(diagDir, "grammar"))
+	}
+	for _, f := range diagFiles {
+		raw, readErr := os.ReadFile(f)
+		if readErr != nil {
+			t.Fatalf("read diag %q: %v", f, readErr)
+		}
+		if strings.Contains(string(raw), secret) {
+			t.Fatalf("secret leaked in diagnostics: %s", string(raw))
+		}
+	}
+}
diff --git a/internal/modules/grammar/prompt.go b/internal/modules/grammar/prompt.go
new file mode 100644
index 0000000..ab6866c
--- /dev/null
+++ b/internal/modules/grammar/prompt.go
@@ -0,0 +1,85 @@
+package grammar
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
+	"gitea.maximumdirect.net/eric/audita/internal/framework/contracts"
+)
+
+type promptSegment struct {
+	ID         int      `json:"id"`
+	Speaker    string   `json:"speaker"`
+	Start      float64  `json:"start"`
+	End        float64  `json:"end"`
+	Text       string   `json:"text"`
+	Categories []string `json:"categories,omitempty"`
+}
+
+type promptTranscriptSection struct {
+	SectionIndex int             `json:"section_index"`
+	Segments     []promptSegment `json:"segments"`
+}
+
+// BuildProposalMessages mirrors the Python grammar-module prompt intent:
+// punctuation/capitalization/spacing cleanup only, with strict meaning guards.
+func BuildProposalMessages(transcript *schema.Transcript, glossary *schema.Glossary) ([]contracts.LLMMessage, error) {
+	glossaryJSON, err := json.MarshalIndent(glossary, "", "  ")
+	if err != nil {
+		return nil, fmt.Errorf("marshal glossary prompt context: %w", err)
+	}
+
+	sectionPayload := promptTranscriptSection{
+		SectionIndex: 0,
+		Segments:     make([]promptSegment, 0),
+	}
+	if transcript != nil {
+		for _, s := range transcript.Segments {
+			sectionPayload.Segments = append(sectionPayload.Segments, promptSegment{
+				ID:         s.ID,
+				Speaker:    s.Speaker,
+				Start:      s.Start,
+				End:        s.End,
+				Text:       s.Text,
+				Categories: append([]string(nil), s.Categories...),
+			})
+		}
+	}
+
+	sectionJSON, err := json.MarshalIndent(sectionPayload, "", "  ")
+	if err != nil {
+		return nil, fmt.Errorf("marshal transcript prompt context: %w", err)
+	}
+
+	system := "You are Audita, a conservative grammar cleanup assistant. Identify only punctuation, capitalization, and spacing cleanup that preserves the same underlying words. Do not change content, substitute words, or rewrite the speaker's phrasing."
+	user := "Review this transcript section and return only grammar cleanup corrections that should be applied.\n\n" +
+		"Rules:\n" +
+		"- Allowed changes are punctuation, capitalization, spacing, and article cleanup only.\n" +
+		"- You may add, remove, or adjust commas, periods, quotation marks, apostrophes, dashes, ellipses, spacing, and capitalization when the underlying words stay the same.\n" +
+		"- You may change the whole-word article \"a\" to \"an\" or \"an\" to \"a\" when the surrounding text otherwise stays the same.\n" +
+		"- Homophone, spoken-form, and mistranscription corrections are handled during a later review stage; do not propose them here.\n" +
+		"- Do not make word substitutions, spelling fixes, homophone fixes, filler cleanup, repetition cleanup, paraphrases, or other semantic rewrites.\n" +
+		"- Do not change one written word into a different written word, except for capitalization changes to the same letters.\n" +
+		"- If a possible correction depends on changing a content word into a different word, omit it here rather than bundling it together with formatting cleanup.\n" +
+		"- Treat glossary names and aliases as protected spellings and context.\n" +
+		"- Do not replace, Anglicize, normalize, lowercase, or otherwise alter protected glossary names or aliases away from their glossary spelling.\n" +
+		"- Preserve canonical glossary capitalization for protected names and aliases, even if they look unusual.\n" +
+		"- If a segment includes categories, treat them as additional transcript context.\n" +
+		"- Use the exact id from the input segment.\n" +
+		"- For returned corrections, original_text must be only the exact text span that needs replacement, not the full segment text unless the whole segment is the replacement span.\n" +
+		"- Choose an original_text span that appears exactly once in the current segment text.\n" +
+		"- corrected_text must be only the replacement text for that span, not the full corrected segment text unless the whole segment is the replacement span.\n" +
+		"- Each returned correction must contain only id, original_text, corrected_text, and confidence.\n" +
+		"- Do not return corrections where original_text and corrected_text are identical.\n" +
+		"- Do not return speaker, start, or end fields.\n" +
+		"- Return only changed segments; do not return entries for unchanged segments.\n" +
+		"- confidence must be between 0.0 and 1.0.\n" +
+		"- If no corrections are needed, return an empty corrections list.\n\n" +
+		fmt.Sprintf("Protected glossary/context:\n%s\n\nTranscript section:\n%s", string(glossaryJSON), string(sectionJSON))
+
+	return []contracts.LLMMessage{
+		{Role: "system", Content: system},
+		{Role: "user", Content: user},
+	}, nil
+}