diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 8379caed6..75cdbd8c7 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed `omp ttsr test <file>` silently evaluating a supplied source file against the text (prose) context when its extension was absent from the hardcoded `SOURCE_FILE_EXT` allowlist, producing a false negative indistinguishable from a non-matching regex. It now emits an explanatory note (in text and `--json` output) when a resolvable file path infers `text`, pointing at `--source tool --tool edit`, and the allowlist gained the .NET family and other common source languages (`cs`, `razor`, `cshtml`, `fs`, `fsx`, `vb`, `sh`, `bash`, `sql`, `zig`, `dart`, `scala`, `ex`, `exs`, `proto`, `tf`) ([#6887](https://github.com/can1357/oh-my-pi/issues/6887)).
+
 ## [17.1.7] - 2026-07-27
 
 ### Fixed
diff --git a/packages/coding-agent/src/cli/ttsr-cli.ts b/packages/coding-agent/src/cli/ttsr-cli.ts
index c20629bf7..2f5f1176f 100644
--- a/packages/coding-agent/src/cli/ttsr-cli.ts
+++ b/packages/coding-agent/src/cli/ttsr-cli.ts
@@ -94,12 +94,18 @@ interface TestReport {
 	evaluated: number;
 	triggered: RuleMatchDetail[];
 	notTriggered: RuleMatchDetail[];
+	/**
+	 * Set when a file path was supplied but the match source was inferred as
+	 * `text` (extension absent from {@link SOURCE_FILE_EXT}), so callers can
+	 * surface why a source file was evaluated against a prose context.
+	 */
+	inferenceNote?: string;
 }
 
 const STDIN_MARKER = "-";
 /** Extensions treated as source files for default tool-context inference. */
 const SOURCE_FILE_EXT =
-	/^\.(ts|tsx|js|jsx|mjs|cjs|rs|py|go|java|kt|swift|c|cc|cpp|h|hpp|rb|php|lua|css|scss|html|json|ya?ml|toml|md|mdc)$/i;
+	/^\.(ts|tsx|js|jsx|mjs|cjs|rs|py|go|java|kt|swift|c|cc|cpp|h|hpp|rb|php|lua|css|scss|html|json|ya?ml|toml|md|mdc|cs|razor|cshtml|fs|fsx|vb|sh|bash|sql|zig|dart|scala|ex|exs|proto|tf)$/i;
 
 const BINARY_PROBE_BYTES = 8192;
 const DEFAULT_MAX_SCAN_BYTES = 5 * 1024 * 1024;
@@ -342,6 +348,14 @@ async function runTest(args: TtsrTestArgs, json: boolean, cwd: string): Promise<
 		args.source ?? (filePath && SOURCE_FILE_EXT.test(path.extname(filePath)) ? "tool" : "text");
 	const tool = args.tool ?? (source === "tool" ? "edit" : undefined);
 
+	// A supplied source file whose extension is unknown falls through to the
+	// text (prose) context, where tool-scoped rules can never match. Surface
+	// that so a false negative reads as a context mismatch, not a bad regex.
+	const inferenceNote =
+		!args.source && filePath && source === "text"
+			? `inferred --source text from '${path.extname(filePath) || filePath}' (not in the source-file extension set); pass --source tool --tool edit to evaluate tool-scoped rules`
+			: undefined;
+
 	const context: TtsrMatchContext = {
 		source,
 		toolName: tool,
@@ -373,6 +387,7 @@ async function runTest(args: TtsrTestArgs, json: boolean, cwd: string): Promise<
 		evaluated: rules.length,
 		triggered,
 		notTriggered,
+		inferenceNote,
 	};
 
 	if (json) {
@@ -390,6 +405,9 @@ function renderTestReport(report: TestReport, verbose: boolean, isolated: boolea
 		`${chalk.bold("TTSR test")} — source=${chalk.cyan(ctxLabel)}${pathLabel} snippet=${chalk.dim(`${report.snippetBytes}b`)}\n`,
 	);
 	process.stdout.write(`${chalk.dim(`  "${report.snippetPreview}"`)}\n\n`);
+	if (report.inferenceNote) {
+		process.stdout.write(`${chalk.yellow(`note: ${report.inferenceNote}`)}\n\n`);
+	}
 
 	if (report.triggered.length === 0) {
 		process.stdout.write(`${chalk.red("No rules triggered.")} (evaluated ${report.evaluated})\n`);
diff --git a/packages/coding-agent/test/cli/ttsr-cli.test.ts b/packages/coding-agent/test/cli/ttsr-cli.test.ts
index 680ab8d72..0d34452fd 100644
--- a/packages/coding-agent/test/cli/ttsr-cli.test.ts
+++ b/packages/coding-agent/test/cli/ttsr-cli.test.ts
@@ -183,6 +183,41 @@ describe("omp ttsr", () => {
 			expect(stdout).toContain("Triggered");
 			expect(stdout).toContain("astCondition");
 		});
+
+		it("infers tool/edit context for a newly-allowlisted .cs file", async () => {
+			captureStreams();
+			const rulePath = await writeTempRule("class", ["tool:edit(*.cs)"]);
+			const snippetPath = await writeTempSnippet("class A {}", "cs");
+			await run({ action: "test", test: { rule: rulePath, file: snippetPath, source: undefined }, json: true });
+			const report = JSON.parse(stdout);
+			expect(report.source).toBe("tool");
+			expect(report.tool).toBe("edit");
+			expect(report.triggered).toHaveLength(1);
+			// A recognized source file needs no context-mismatch note.
+			expect(report.inferenceNote).toBeUndefined();
+		});
+
+		it("emits an inference note when a supplied file path falls through to text source", async () => {
+			captureStreams();
+			const rulePath = await writeTempRule("class", ["tool:edit(*.cs)"]);
+			const snippetPath = await writeTempSnippet("class A {}", "unknownext");
+			await run({ action: "test", test: { rule: rulePath, file: snippetPath, source: undefined }, json: true });
+			const report = JSON.parse(stdout);
+			expect(report.source).toBe("text");
+			expect(report.inferenceNote).toContain(".unknownext");
+			expect(report.inferenceNote).toContain("--source tool --tool edit");
+			// The tool-scoped rule is a false negative here — the note explains why.
+			expect(report.triggered).toHaveLength(0);
+		});
+
+		it("omits the inference note when --source is explicit", async () => {
+			captureStreams();
+			const rulePath = await writeTempRule("class", ["tool:edit(*.cs)"]);
+			const snippetPath = await writeTempSnippet("class A {}", "unknownext");
+			await run({ action: "test", test: { rule: rulePath, file: snippetPath, source: "text" }, json: true });
+			const report = JSON.parse(stdout);
+			expect(report.inferenceNote).toBeUndefined();
+		});
 	});
 
 	describe("list", () => {