Spec-Driven C#: Process

Synopsis:

This thread follows the C# implementation, the third of the four, written from a parent specification that six reviews had already settled.

One prompt record covering six turns, against the 14 the C++ thread carries. The difference is less a gap in the evidence than a difference in what there was to record.
Section 2 lists the four things the parent specification delegates, and what C# answers for each.

Four answers changed the shape of the code, and the language forced every one of them.

No free functions and no Result type, so the four entry points are static methods and parsing is a TryParse with two out parameters.
The terminator rule was written with this language in mind - Console.WriteLine is what sent it up to the parent specification.
No destructor to hang a flush on, so the guarantee lives in the caller's using rather than in the type.
One assembly runs on both platforms, so the platform test is evaluated at run time where the siblings decide at compile time.

Two things about this thread's evidence are named rather than left to a reader.

It took the documents-alone route, but both siblings were already in context from earlier work in the same session - weaker evidence than a clean-room derivation, and saying so is worth more than a claim the record cannot support.
The suites passed first time, which is a weaker result than it sounds. The C++ first run failed eight assertions and found a real contradiction between two specification sections.

1. What the Records Show

The C# implementation carries one Prompts_*.md record, Prompts_Build_CSharp_TextFinder.md, and Page_Structure.md §8 puts it on this page. It covers six turns, from the creation of the C# folder through the four component specifications, the nine projects, the four suites, the demonstration, and the ignore rules.

One record against the C++ thread's 14. The difference is not a gap in the evidence so much as a difference in what there was to record: C++ built its five documents over dozens of turns and six reviews, and C# wrote four component specifications in one turn from a parent specification that six reviews had already settled.

Page	Records	What they cover
Process (this page)	1	The folder, the structure document, the four component specifications, the code, the suites, and the demonstration
Structure	0	Its turn is recorded here, the whole thread having one record
Entry	0	As above
Cmdline	0	As above
Dirnav	0	As above
Output	0	As above
Testing	0	As above
Demonstration	0	As above

The record quotes user prompts verbatim and summarizes replies, noting tool calls as effects rather than transcribing them. It is a record, not an input to code: Constitution.md rule 1 names Spec*.md and *Structure.md and nothing else.

2. What the Parent Left to C#

Spec_TextFinder.md §2 states what it fixes and what it delegates. What it fixes is what a user sees on stdout: the blocks and announcements of §3.4, the help text of §5.1, the option listing of §5.3, and the exit codes. Four things it hands to a component specification, and until this thread had one, those four had nowhere to be settled.

Delegated	Section	What C# answers
The argument vector's type and encoding	§4	`string[]`, already decoded by the runtime, holding the arguments alone. No encoding limit follows, and no exit code
The skip-list extension point's signature	§3.5	`private static void AddSkipDirectory(string name)`, declared in the binary and callable from nothing else
The wording of anything reaching stderr	§5.2	§5.2's seven reason lines adopted unchanged, six fixed in the Cmdline specification and the seventh in Entry's, plus `cannot initialize output`
Which standard-library facility implements each rule	§2	Named call by call, with eight framework methods rejected by name. Section 3 covers the four that matter most

Writing those decisions into code rather than into a document would have settled them where rule 1 says they cannot be settled, so the four component specifications came first and the code derived from them. That ordering is the whole of what "spec-driven" means here, and it is the one thing this thread has in common with the other two despite sharing almost no standard-library call with either.

3. Where C# Answered Differently

Four answers changed the shape of the code rather than a detail of it.

3.1 No Free Functions

The C++ implementation exports parse, usageLine, helpText, and optionsText at global scope, and the Rust one exports four functions from a module. C# has neither, so the four are static methods of one static class, CommandLine, and the namespace carries the component name.

That forced a second naming decision the siblings never face. A class sharing its namespace's name makes every using of that namespace ambiguous to read, so the types inside a component carry their own names rather than the component's: the sink is StdoutSink in namespace CSharp_TextFinder_Output, where the C++ sink is the class Cpp_TextFinder_Output.

The parse entry is a TryParse with two out parameters rather than a returned result. C++ has std::expected and Rust has Result; the base class library has neither, and a malformed command line is something the user typed, so it is an ordinary outcome rather than an exceptional one. The NotNullWhen attributes are what let a caller compiling with nullable reference types use either out value without a null check.

3.2 The Terminator Rule Was Written for This Language

Spec_TextFinder.md §3.4 obliges an implementation to stop its runtime translating the LF terminator to CRLF. That rule began life in the C++ Output specification, binding C++ alone, and the cross-document review promoted it to the parent with the C# case as its argument: Console.WriteLine terminates with Environment.NewLine, which is CRLF on Windows, so the framework's most obvious way to write a line is the one the specification forbids.

The review made that argument before any C# code existed. This implementation is where it gets tested, and the answer is a StreamWriter over Console.OpenStandardOutput() with NewLine set to "\n" and a UTF8Encoding that emits no byte-order mark. Console.Out is not used at all, so nothing the framework configures on it reaches this program's output. The integration suite checks the bytes rather than the characters, and finds no CR and no BOM.

Three implementations now meet one requirement three ways. C++ calls _setmode(1, _O_BINARY) and can fail trying; Rust does nothing, its standard output performing no translation on any platform; C# replaces the writer. A rule promoted to the parent on a prediction about one language turned out to bind that language most tightly.

3.3 A Flush With No Destructor to Hang It On

The C++ sink flushes in its destructor and the Rust sink in Drop, and both specifications pair that with a rule on the binary: every exit is a return, never a call to std::exit or std::process::exit, or the buffer would be discarded.

C# has no destructor that runs at scope exit. A finalizer is not a substitute, because the runtime is free never to run one before the process ends, which would make a short search lose its output. The sink therefore implements IDisposable and Main holds it in a using statement, so the guarantee lives in the caller rather than in the type.

One consequence reached the startup sequence and is worth naming, because the obvious code does not work. A using declaration on the constructor call would put the construction inside the block it introduces, where a catch cannot reach it - and construction is exactly what can fail with the exit code 2 that §3.4 fixes. The construction therefore sits in its own try and the using statement follows, which is the C# counterpart of the std::optional the C++ binary uses for the same reason.

3.4 One Assembly, Two Platforms

Spec_TextFinder.md §3.2 and §5 make extension and skip-list comparison case-sensitive on POSIX and case-insensitive on Windows. C++ answers with #ifdef _WIN32 and Rust with #[cfg(windows)], and both decide at compile time.

A .NET assembly is compiled once and runs on both platforms, so a conditional-compilation test here would fix the behavior of the machine that built the assembly rather than the machine that runs it. The test is OperatingSystem.IsWindows(), evaluated at run time and held in one field. That field is the only place in CSharp_TextFinder_Dirnav where the platform changes behavior.

The comparison itself is StringComparison.OrdinalIgnoreCase or StringComparison.Ordinal, never a culture-sensitive form. Under a Turkish culture a culture-sensitive fold of I and i differs from the invariant one, which would make the same tree and the same /p list select different files on two machines of the same platform. The binary enables InvariantGlobalization, so a culture-sensitive comparison added later fails visibly rather than behaving differently in two places.

4. Three Corrections the Code Forced

Writing the code found three things the specifications had wrong or had left out. Each was fixed in the document first, which is what rule 1 requires and what makes the fix visible to the next reader rather than only to the compiler.

A third exception type. Dirnav's rule 7 named IOException and UnauthorizedAccessException as the failures a filesystem call resolves to an announcement. ArgumentException joined them: the framework reports a path string the platform will not accept by argument validation rather than by a failed call, and an uncaught one would end the walk.
A literal that depended on its own file. The Cmdline specification had the help body as a raw string literal, which reads better in the source and carries the line terminators of the file it is written in. An editor or a .gitattributes rule that rewrote that source to CRLF would change what the program prints, and §5.1 fixes the text while §3.4 fixes the terminator. The body became a string[] joined with "\n", which makes the terminator a decision of the library rather than a property of its encoding.
A limit on the root-kind test. §3.2 has a root that resolves to neither a regular file nor a directory announced rather than searched, and FileAttributes carries no flag distinguishing a regular file from a FIFO, a socket, or a device node. The specification now records that every entry which is neither a directory nor a reparse point is treated as a regular file, so such an entry draws cannot open through the failed read of rule 7 rather than through the kind test of rule 1. The announcement §3.2 asks for still appears; what differs is what it reports.

Two mechanical problems came up in the same turn and neither was a specification defect. The first build failed on one error, CS0103: The name 'CultureInfo' does not exist, from a using removed while its one consumer survived; that consumer was doing culture-aware formatting on a string that needed none, and it became concatenation. And three characters of the /p trim set - horizontal tab, vertical tab, and form feed - had been written as literal control characters rather than escapes, which makes a source file depend on bytes no reader can see. They became (char)0x09, (char)0x0B, and (char)0x0C, and the BOM test in Dirnav became (char)0xFEFF, on the ground that §5 names those characters by code point and three of the six have no readable literal form.

5. The State of the Record

Two things about this thread's evidence are worth naming rather than leaving to a reader who counts <details> blocks.

This thread took the documents-alone route, and the claim needs a qualifier. Constitution.md rule 1 permits a sibling implementation to serve as an example where a user prompt asks for it, and the prompt that produced this code named the Constitution and the structure document rather than a sibling. No C++ or Rust source was consulted while the C# sources were written. But both siblings' specifications and sources were already in context from the same session's earlier work on the Rust thread's pages, and that cannot be undone. This is therefore weaker evidence that the specifications are sufficient than a clean-room derivation would be, and saying so is worth more than a claim the record cannot support.

One turn earlier the same session had amended rule 1 to add that permission, because the Rust sources had been written with the C++ implementation in view under a rule that excluded example code without qualification. The Constitution page covers the amendment and the two limits that came with it. The C# structure document was written under the request that permission is gated on; the C# code was not.

The suites passed on their first run, and that is a weaker result than it sounds. 157 checks across four suites, no failures, no warnings from nine projects. The C++ implementation's first run failed eight integration assertions on a CRLF difference, and that failure is the more instructive outcome: it found a real contradiction between two specification sections. A first run that passes says the code matches the specification it was written from hours earlier, by the same author, which is a narrower claim. The Testing page names the four claims no suite reaches.

6. Prompt Records

The one record this thread carries, in full. It runs from the creation of the C# folder through the structure document, the two questions that stopped the implementation turn before it started, the four component specifications, the nine projects, the four suites, the demonstration, and the ignore rules.

Prompts_Build_CSharp_TextFinder.md

# Prompts and Replies — Building CSharp_TextFinder

This file records the turns that produced the C# TextFinder, from the creation of this folder through the specifications, the code, the suites, and the demonstration. The numbering is this record's own: the turns ran consecutively at the end of a session of 2026-09-15 and 2026-09-16 whose earlier work was the Rust thread's `Spec_Driven_Design_*.html` pages and an amendment to [Constitution.md](../Constitution.md), neither of which is recorded here.

That amendment matters to turn 2 and is summarized rather than assumed. Rule 1 had excluded "example code" without qualification, which made a later language thread's only lawful source its own specifications. It now reads that an implementation already in this project may serve as an example for a later one **if requested by user prompt**, with the specifications remaining the authority and an ambiguity still a question to ask rather than a gap to fill from what the sibling did. Turn 2's prompt is such a request. Turn 4's answer declines it.

User prompts are quoted verbatim. Assistant replies are summarized from the actual responses; tool calls are noted as effects rather than transcribed.

---

## Turn 1

### User

> Create Project subfolder CSharp_Spec_driven_TextFinder

### Assistant

Created [CSharp_Spec_driven_TextFinder/](.) beside the C++ and Rust folders, and noted that the name matches [Page_Structure.md](../Page_Structure.md) §0, which fixes `CSharp` as the `[lang]` token for the C# thread. Reported that the directory was empty, so git would not track it until a file landed there.

---

## Turn 2

### User

> Create CSharp_TextFinder_Structure.md using Cpp_TextFinder_Structure as an example, but honor the constraints of the C# language

### Assistant

Read [Cpp_TextFinder_Structure.md](../Cpp_Spec_driven_TextFinder/Cpp_TextFinder_Structure.md) and the parent specification's §3.5, §6, and §6.1, then wrote [CSharp_TextFinder_Structure.md](CSharp_TextFinder_Structure.md) with the same five sections and the same three-libraries-and-one-binary shape: `CSharp_TextFinder_Dirnav` references `CSharp_TextFinder_Cmdline`, `CSharp_TextFinder_Output` references `CSharp_TextFinder_Dirnav`, and nothing references Output but the binary.

Nine places where C# forced a different answer rather than a renamed one, each written into the document:

1. C# has no free functions, so Cmdline's parse entry, usage line, help text, and option listing are static methods of one static class, `CommandLine`.
2. The seam is `interface IOutput`, and the generic parameter is described honestly: a C# generic over a reference type shares one compiled body, so the constrained call is not devirtualized the way a C++ template instantiation or a Rust monomorphization is. It buys the compile-time bound and test substitutability, not a direct call.
3. Types carry their own names rather than the component's — the sink is `StdoutSink` in namespace `CSharp_TextFinder_Output` — because a class sharing its namespace's name makes every `using` of that namespace ambiguous to read.
4. `Console.WriteLine` terminates with `Environment.NewLine`, CRLF on Windows, so §3.4 rules it out. A `StreamWriter` over `Console.OpenStandardOutput()` with `NewLine` set to `"\n"` replaces it. This is the case the cross-document review cited when it promoted the terminator rule from the C++ Output specification to the parent.
5. C# has no destructor that runs at scope exit, so the sink implements `IDisposable` and `Main` holds it in a `using` statement. A finalizer is explicitly not relied on, the runtime being free never to run one.
6. `Main`'s `string[] args` holds the arguments alone, where C++'s `argv[0]` and Rust's first `args_os()` element hold the executable. The bare command line of §3.1 is therefore an empty array, and the parser scans from index 0.
7. A `string` is UTF-16 and the runtime decodes the command line before `Main` runs, so the undecodable-argument case the Rust implementation defines has no counterpart and needs no exit code.
8. The garbage collector keeps the sink, the skip list, and the commands alive, so the lifetime rule C++ states in prose and Rust enforces with a borrow checker has nothing to enforce.
9. A `static` field needs no lock and no interior-mutability type, so the `thread_local!` and `RefCell` pair the Rust implementation requires has no counterpart.

Dependencies land differently too, and the document says so: `System.Text.RegularExpressions.Regex` ships with the framework, so C# declares no package reference at all where Rust needs the `regex` crate and C++ needs an undocumented CMake opt-in token.

Flagged two things. The four `Spec_CSharp_*.md` links were forward references to files that did not exist. And `net8.0` with C# 12 was chosen against a floor of SDK 8.0.100, with 8.0.319 and 10.0.100 both present on the machine, offering `net10.0` instead.

---

## Turn 3

### User

> create the C# implementation using the Project constitution, and CSharp_TextFinder_Structure.md

### Assistant

Reported that the Constitution makes this a two-step job before starting it. Rule 1 has code derive from `Spec*.md` and `*Structure.md`, and the C# thread held the structure document and the parent specification but none of its own component specifications — and the parent deliberately delegates four things to a component spec: the argument vector (§2), the exact `addSkipDirectory` name, parameter, and return type (§3.5), the stderr wording for all seven reason lines (§2, §5.2), and which standard-library call sits behind each traversal and admission rule (§2). Writing those decisions straight into code would settle them where rule 1 says they cannot be settled, and the Constitution's own note says to ask rather than fill the gap.

Also noted that the prompt named the Constitution and the structure document and not the C++ or Rust implementation, so rule 1's sibling permission — gated on the prompt asking for it — was not engaged, and C# would be written from the documents alone unless told otherwise.

Asked two questions rather than guessing: how far the pass should go, and which sibling material was admissible.

---

## Turn 4

### User

Answered both:

> How far should this go in one pass? — Specs, then code, then suites
>
> Which sibling material, if any, may I draw on? — Documents alone

### Assistant

**Structure first.** Amended [CSharp_TextFinder_Structure.md](CSharp_TextFinder_Structure.md)'s Build section before writing any project file, since the layout is a structural decision and rule 1 puts the document ahead of the code. It gained four bullets: each component holds its `Spec_*.md`, its project file, its sources under `src/`, and — for the three libraries — its unit-test project under `test/`, which §6.2 asks to live beside the code it tests; the integration suite, the demonstration, and the three runners sit at the solution root; each library project carries one `<Compile Remove="test/**" />` item, because the .NET SDK compiles every `.cs` beneath a project and would otherwise build a suite into the shipped assembly; and no third-party test framework is introduced, so each suite is a console project whose `Main` returns the number of checks that failed and `dotnet test` is not used.

**Four component specifications**, each naming what the parent delegates to it:

- [Spec_CSharp_TextFinder_Cmdline.md](CSharp_Spec_driven_Cmdline/Spec_CSharp_TextFinder_Cmdline.md), 137 lines. `TryParse` with `NotNullWhen` attributes rather than a result type or an exception, since the `Try` pattern is how C# expresses a failure that is not exceptional and the base class library has no `expected`. The six §5.2 reason lines adopted unchanged and fixed here. The scan beginning at index 0. `bool.TryParse` rejected by name for trimming and accepting more than §5 admits, `string.Trim()` for trimming every character Unicode calls whitespace, `string.TrimStart('.')` for stripping every leading dot where §5 strips one, and `bool.ToString()` for returning `"True"`.
- [Spec_CSharp_TextFinder_Dirnav.md](CSharp_Spec_driven_Dirnav/Spec_CSharp_TextFinder_Dirnav.md), 131 lines. `File.GetAttributes` for an entry's kind, with `Directory.Exists` and `File.Exists` rejected by name because both follow a link and both answer `false` for an entry that exists and cannot be opened. `Directory.EnumerateFileSystemEntries` for one level lazily, with `GetFileSystemEntries`, `GetFiles` plus `GetDirectories`, and `RecurseSubdirectories = true` each rejected by name. `OperatingSystem.IsWindows()` at run time, because a .NET assembly is built once and runs on both platforms, so C++'s `#ifdef _WIN32` and Rust's `#[cfg(windows)]` have no counterpart. `Encoding.UTF8.GetString` rejected in the sharpest terms in the document: its fallback substitutes U+FFFD and reports nothing, so every file would pass §3.3's UTF-8 test and the UTF-16-file-of-ASCII-text case §3.3 names would be searched as mojibake.
- [Spec_CSharp_TextFinder_Output.md](CSharp_Spec_driven_Output/Spec_CSharp_TextFinder_Output.md), 115 lines. The `StreamWriter` with `NewLine` of `"\n"`, `AutoFlush` false, and a `UTF8Encoding` that emits no byte-order mark. The one-sink rule behind a private static `bool`, and why a static mutable field is the right mechanism for a process-wide resource where Rust needs a `thread_local!` `Cell` to escape a `Sync` bound. Disposal as the whole of the flush mechanism.
- [Spec_CSharp_TextFinder_Entry.md](CSharp_Spec_driven_TextFinder_Entry/Spec_CSharp_TextFinder_Entry.md), 111 lines. An eight-step startup sequence with no argument-decoding step, `AddSkipDirectory(string)` returning `void` as §3.5's shape in C# spelling, the two code-2 strings, and the `try` around construction sitting outside the `using` statement so that a `catch` can reach the failure and the disposal is still guaranteed — the C# counterpart of the `std::optional` the C++ binary uses for the same reason.

**Nine projects**, built as one solution: three libraries, the binary with `AssemblyName` of `CSharp_TextFinder` and `InvariantGlobalization` enabled, three unit-test consoles, the integration console, and the demonstration console. Three runners, each building the solution first and reporting a suite that was never built as a failure rather than skipping it.

**Three corrections the code forced, each made in the document first.** `ArgumentException` joined Dirnav rule 7's caught types, covering a path string the platform will not accept. The help body became a joined `string[]` rather than a raw string literal, because a raw literal carries the line terminators of the file it is written in and an editor or a `.gitattributes` rule that rewrote the source to CRLF would change what the program prints. And a limit was recorded rather than left to be found: `FileAttributes` carries no flag distinguishing a regular file from a FIFO, a socket, or a device node, so every entry that is neither a directory nor a reparse point is treated as a regular file, and such an entry draws `cannot open` through rule 7's failed read rather than through rule 1's kind test.

**Two mechanical problems.** The first build failed on one error, `CS0103: The name 'CultureInfo' does not exist`, from a `using` removed while its one consumer survived; the consumer was a `string.Create` call doing culture-aware formatting on a string that needed none, and it became concatenation. And three characters — horizontal tab, vertical tab, and form feed — had been written into the `/p` trim set as literal control characters rather than escapes, which made the source depend on bytes no reader can see. They were rewritten as `(char)0x09`, `(char)0x0B`, and `(char)0x0C`, and the BOM test in Dirnav as `(char)0xFEFF`, on the ground that §5 names those characters by code point and three of the six have no readable literal form. A scan of every `.cs` file confirmed none remained.

**Results.** All nine projects build with zero warnings and zero errors. 67 Cmdline checks, 31 Dirnav, 7 Output, and 52 integration — 157 in total, every one passing on its first run. The demonstration ran 11 invocations and exited 0, and its capture was saved to [Demo_9-16-2026.md](Demo_9-16-2026.md) per §6.2's requirement that a capture state its date. Verified separately that stdout carries no byte-order mark and no CR byte.

**One disclosure.** The choice of "documents alone" was honored in the sense that the C# sources were written from the parent specification and the structure document, and no C++ or Rust source was consulted while writing them. But the C++ and Rust specifications and sources were already in context from the same session's earlier work on the Rust pages, and that cannot be undone. This is therefore weaker evidence that the specifications are sufficient than a clean-room derivation would be, and the C# thread's Process page should say so rather than claim one.

Finally, added a `.gitignore` inside this folder for `bin/` and `obj/`, since rule 2 bars modifying the repository root file without an explicit request naming it, and flagged that the Rust `target/` directory was ignored nowhere.

---

## Turn 5

### User

> fix it

### Assistant

Read the request as naming the repository root `.gitignore`, which was the subject of the sentence it answered, and said so rather than assuming it. Added the Rust `target/` entry and two scoped C# globs, and deleted the local file so the rule lives in one place — which is where the C++ entry had been moved by an earlier request:

    Code/Projects/Spec_driven_TextFinder/Cpp_Spec_driven_TextFinder/build/
    Code/Projects/Spec_driven_TextFinder/Rust_Spec_driven_TextFinder/target/
    Code/Projects/Spec_driven_TextFinder/CSharp_Spec_driven_TextFinder/**/bin/
    Code/Projects/Spec_driven_TextFinder/CSharp_Spec_driven_TextFinder/**/obj/

The `**/` is what covers all nine C# projects, the three unit-test projects nested a level deeper under their components included. Every entry is a scoped path rather than a bare directory name, so the rest of the site repository is unaffected. Verified with `git check-ignore` against one artifact from each tree, then with `git status --untracked-files=all` over the project, which reported 30 untracked files with no `bin`, `obj`, `target`, or `build` path among them.

---

## Turn 6

### User

> create Prompts_Build_CSharp_TextFinder.md with all the prompts and replies for creating the C# implementation.

### Assistant

Created this file, [Prompts_Build_CSharp_TextFinder.md](Prompts_Build_CSharp_TextFinder.md), covering the six turns from the creation of this folder through the specifications, the code, the suites, the demonstration, and the ignore rules. [Page_Structure.md](../Page_Structure.md) §8 decides a record's thread by the directory level it was produced at, so this one sits in the C# folder and belongs to the C# thread; its §8 table assigns a `Prompts_Build_[lang]_TextFinder.md` to that thread's Process page, which does not exist yet.