Build the template engine — board-as-template instantiation

A template is a board folder the ordinary loader reads — no second
schema, no Swift catalog. BoardTemplate became exactly that: a loaded
BoardModel with chooser-facing derivations, the lane-title stub gone.
TemplateEngine instantiates by the copy-remint-restamp walk: .git and
.trash excluded at top level only — both names mean something at a
board root and nowhere else, and .gitignore must survive — every
materialized folder reminted, created/modified stamped fresh (born
today, not forked), modified-by cleared, the template: key carried
inert, the blurb and style inherited, and loose card files normalized
at this import boundary per the paste precedent so a new board never
opens with a notice about a mess its own birth made. Legacy deleted:
keys copy through verbatim to the one migrator — stripping would
resurrect, skipping would destroy. Atomicity is construct-then-clean:
a sibling temp can be sandbox-refused and a cross-volume rename is
just a second copy, so the call removes what it created on every
non-board exit and never touches an occupied destination. The
cancellable per-item walk extracted into BoardTreeCopy serves
Duplicate and instantiation with two parameters — top-level exclusions
and folder-attribute carriage, the only axes they differ on.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY
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import Foundation
import Testing
@testable import Kanban
/// Template **instantiation** "create a board from this template", on disk (09-templates.md
/// Instantiation).
///
/// The round trip is the heart of it: instantiate, then load the result through the ordinary
/// `BoardLoader` and ask whether what came back is a board born today. Everything 09 promises is an
/// assertion about those bytes
///
/// - copied, **minus `.trash/` and `.git`**, and minus nothing else;
/// - **fresh GUIDs** at every level no identity survives from the template;
/// - **fresh `created`/`modified`**, `modified-by` cleared born today, not forked;
/// - `title` = the name the user typed into the save panel;
/// - `template:` carried and inert; strays, bodies and attachment bytes verbatim.
///
/// plus the promise that makes it safe to run at all: **nothing half-made is ever left at the
/// destination**, whether the user cancelled or the disk said no.
// MARK: - Helpers
/// `writeFailure`'s twin for the engine's two-outcome vocabulary.
private func instantiationFailure(_ operation: () throws -> Void) -> TemplateEngine.Failure? {
do {
try operation()
Issue.record("expected the instantiation to fail, but it succeeded")
return nil
} catch let failure as TemplateEngine.Failure {
return failure
} catch {
Issue.record("expected a TemplateEngine.Failure, got \(error)")
return nil
}
}
/// Every path under `root`, root-relative, hidden entries included.
private func tree(of root: URL) -> Set<String> {
var paths: Set<String> = []
let walker = FileManager.default.enumerator(at: root, includingPropertiesForKeys: nil, options: [])
while let url = walker?.nextObject() as? URL {
paths.insert(url.path.replacingOccurrences(of: root.path + "/", with: ""))
}
return paths
}
/// Every UUID-shaped folder name under `root` the identities a copy either kept or reminted.
private func identities(under root: URL) -> Set<String> {
Set(tree(of: root)
.flatMap { $0.split(separator: "/").map(String.init) }
.filter(BoardLoader.isUUIDShaped)
.map { $0.lowercased() })
}
/// The two GUIDs the bundled Basic template ships with hard-coded on purpose: "no id survives
/// from the template" is only an assertion if the test knows the ids it is looking for.
private enum BundledBasic {
static let toDo = "3f2a9c41-6b0e-4d7a-9f31-2c8b5e0a7d14"
static let done = "8d3b1f22-4a7c-4e59-8b06-1d9f3c2e6a85"
}
private func bundledBasic() throws -> BoardTemplate {
try #require(TemplateEngine.bundledTemplates().first { $0.slug == "basic" })
}
// MARK: - The hand-built template
/// A template carrying everything 09 and 01 have a rule about: the two exclusions, a legacy
/// `deleted:` key, strays at board and lane level, a symlink, an attachment, and a loose file
/// beside a card's `index.md`.
private struct FixtureTemplate {
let fixture: WriterFixture
let root: URL
static let name = "Fixture.kanban"
static let blurb = "A fixture blurb, which becomes the new board's description.\n"
init() throws {
fixture = try WriterFixture()
root = fixture.url(Self.name)
let path = Self.name
// The board: a template key, an agent overlay, old stamps, and someone else's attribution.
try fixture.item(path, """
---
schema: 1
title: Fixture Template
icon: rectangle.split.3x1
iconColor: fern
template: {order: 42}
project: lanework
created: 2026-01-01T09:00:00Z
modified: 2026-02-02T09:00:00Z
modified-by: claude
---
\(Self.blurb)
""")
// Board-level strays "the copy is literal apart from the stated exclusions".
try fixture.file("\(path)/CLAUDE.user.md", Data("board instructions\n".utf8))
try fixture.file("\(path)/.gitignore", Data(".DS_Store\n".utf8))
// The two exclusions.
try fixture.file("\(path)/.git/HEAD", Data("ref: refs/heads/main\n".utf8))
try FileManager.default.createDirectory(
at: root.appendingPathComponent(".git/objects", isDirectory: true),
withIntermediateDirectories: true
)
try fixture.item("\(path)/.trash/\(Ident.card4)", Item.rich(order: "1024", title: "Thrown Away"))
// A symlink, never traversed, copied as a link.
try FileManager.default.createSymbolicLink(
atPath: root.appendingPathComponent("link.md").path,
withDestinationPath: "../outside.txt"
)
// A lane with a starter card: an attachment, a loose file, and a body.
try fixture.item("\(path)/\(Ident.lane1)", Item.rich(order: "1024", title: "To Do"))
try fixture.item("\(path)/\(Ident.lane1)/\(Ident.card1)", Item.rich(order: "1024", title: "Starter"))
try fixture.file("\(path)/\(Ident.lane1)/\(Ident.card1)/attachments/shot.png", Data([0x01, 0x02, 0x03]))
try fixture.file("\(path)/\(Ident.lane1)/\(Ident.card1)/notes.txt", Data("loose\n".utf8))
// A card an older app version tombstoned in place the legacy `deleted:` key.
try fixture.item("\(path)/\(Ident.lane1)/\(Ident.card2)", """
---
schema: 1
title: Legacy Tombstone
order: 2048
deleted: 2026-01-01T00:00:00Z
---
still here
""")
// A second lane with a stray folder of its own lane-level strays stay verbatim.
try fixture.item("\(path)/\(Ident.lane2)", Item.rich(order: "2048", title: "Done"))
try fixture.file("\(path)/\(Ident.lane2)/notes/scratch.md", Data("scratch\n".utf8))
}
func tearDown() { fixture.tearDown() }
func template() throws -> BoardTemplate {
switch TemplateEngine.load(templateAt: root, origin: .user) {
case let .success(template): return template
case let .failure(error): throw error
}
}
/// Where an instantiation lands a sibling of the template inside the same temp root, which is
/// also what makes "nothing was left behind" a one-line assertion.
func destination(named name: String = "New Board.kanban") -> URL {
fixture.url(name)
}
}
// MARK: - Round trip
@Suite("TemplateEngine — the bundled round trip")
struct TemplateEngineRoundTripTests {
@Test("Instantiating Basic produces a board that loads clean")
func basicLoadsClean() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Q3 Planning.kanban")
try TemplateEngine.instantiate(template: try bundledBasic(), to: destination, title: "Q3 Planning")
let result = try BoardLoader.load(boardRoot: destination)
#expect(result.warnings.isEmpty, "a board the app just instantiated must load without a murmur")
#expect(result.looseCardFiles.isEmpty)
#expect(result.legacyTombstones.isEmpty)
#expect(result.model.lanes.map { $0.title.value } == ["To Do", "Done"])
#expect(result.model.lanes.map(\.order) == [1024, 2048])
}
@Test("The title is the document name the user chose, not the template's")
func titleIsTheChosenName() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Q3 Planning.kanban")
try TemplateEngine.instantiate(
template: try bundledBasic(),
to: destination,
title: TemplateEngine.documentName(of: destination)
)
// 01-storage-format.md § Board naming: display name and folder name start out matching.
#expect(try BoardLoader.load(boardRoot: destination).model.title.value == "Q3 Planning")
}
@Test("An extension-less location is as legal a board, and keeps its whole name as the title")
func extensionlessLocationWorks() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Plain")
try TemplateEngine.instantiate(
template: try bundledBasic(),
to: destination,
title: TemplateEngine.documentName(of: destination)
)
#expect(try BoardLoader.load(boardRoot: destination).model.title.value == "Plain")
}
@Test("No id survives from the template — every lane folder is a fresh mint")
func everyIdentityIsReminted() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Minted.kanban")
try TemplateEngine.instantiate(template: try bundledBasic(), to: destination, title: "Minted")
let minted = identities(under: destination)
#expect(minted.count == 2)
#expect(minted.isDisjoint(with: [BundledBasic.toDo, BundledBasic.done]),
"template GUIDs are inert — instantiation remints at its own boundary")
#expect(minted.allSatisfy { $0 == $0.lowercased() && UUID(uuidString: $0) != nil })
}
@Test("Born today: created and modified are fresh, and modified-by is absent")
func stampsAreFresh() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Born.kanban")
let start = Date()
try TemplateEngine.instantiate(template: try bundledBasic(), to: destination, title: "Born")
let model = try BoardLoader.load(boardRoot: destination).model
let template = try bundledBasic().model
let boardCreated = try #require(model.created.value)
#expect(boardCreated.timeIntervalSince(start) > -2, "born today, not forked from the template")
#expect(boardCreated != template.created.value)
#expect(try #require(model.modified.value).timeIntervalSince(start) > -2)
#expect(model.modifiedBy.isMissing)
for lane in model.lanes {
#expect(try #require(lane.created.value).timeIntervalSince(start) > -2)
#expect(try #require(lane.modified.value).timeIntervalSince(start) > -2)
#expect(lane.modifiedBy.isMissing)
}
}
@Test("The template: key is carried onto the instantiated board, inert")
func templateKeyIsCarriedInert() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Inert.kanban")
try TemplateEngine.instantiate(template: try bundledBasic(), to: destination, title: "Inert")
let model = try BoardLoader.load(boardRoot: destination).model
let template = try bundledBasic().model
#expect(model.template == template.template,
"kept, ignored, and preserved like any unknown key")
#expect(model.document.body == template.document.body,
"the blurb becomes the new board's description, byte for byte")
}
@Test("The icon and its tint are inherited from the template")
func iconIsInherited() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let destination = fixture.url("Styled.kanban")
let basic = try bundledBasic()
try TemplateEngine.instantiate(template: basic, to: destination, title: "Styled")
let model = try BoardLoader.load(boardRoot: destination).model
#expect(model.icon.value == basic.model.icon.value)
#expect(model.iconColor.value == basic.model.iconColor.value)
}
@Test("The bundled template itself is never touched by instantiating it")
func theTemplateIsReadOnly() throws {
let fixture = try WriterFixture()
defer { fixture.tearDown() }
let basic = try bundledBasic()
let before = tree(of: basic.url)
let bytes = try Data(contentsOf: basic.url.appendingPathComponent("index.md"))
try TemplateEngine.instantiate(template: basic, to: fixture.url("Copy.kanban"), title: "Copy")
#expect(tree(of: basic.url) == before)
#expect(try Data(contentsOf: basic.url.appendingPathComponent("index.md")) == bytes)
}
}
// MARK: - The hand-built template
@Suite("TemplateEngine — a hand-dropped template's edges")
struct TemplateEngineFixtureTests {
@Test("`.git` and `.trash/` are the two exclusions, and they are the only ones")
func theTwoExclusionsAreExcluded() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
let paths = tree(of: destination)
#expect(!paths.contains { $0 == ".git" || $0.hasPrefix(".git/") },
"a template is content, not history — no board is silently born in git mode")
#expect(!paths.contains { $0 == ".trash" || $0.hasPrefix(".trash/") },
"a new board isn't born with trash")
// And everything else did come along `.gitignore` included, which is a stray the
// exclusion must not swallow: the two exclusions are exact names, not prefixes.
#expect(paths.contains("CLAUDE.user.md"))
#expect(paths.contains(".gitignore"))
#expect(paths.contains("link.md"))
#expect(paths.contains { $0.hasSuffix("notes/scratch.md") }, "a lane-level stray folder is a resident")
}
@Test("Strays and attachments arrive byte for byte")
func straysAndAttachmentsAreVerbatim() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
#expect(try Data(contentsOf: destination.appendingPathComponent("CLAUDE.user.md"))
== Data("board instructions\n".utf8))
#expect(try Data(contentsOf: destination.appendingPathComponent(".gitignore"))
== Data(".DS_Store\n".utf8))
let card = try #require(cardFolders(under: destination).first { folder in
FileManager.default.fileExists(atPath: folder.appendingPathComponent("attachments/shot.png").path)
})
#expect(try Data(contentsOf: card.appendingPathComponent("attachments/shot.png")) == Data([0x01, 0x02, 0x03]))
}
@Test("A card's body survives the fresh stamps — frontmatter is edited, bytes are not rewritten")
func bodiesSurviveTheRestamp() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
let model = try BoardLoader.load(boardRoot: destination).model
let starter = try #require(model.lanes.flatMap(\.cards).first { $0.title.value == "Starter" })
#expect(starter.document.body == "Starter body — with *markdown*.\n")
#expect(starter.document.value(for: "project") == .string("lanework"),
"unknown keys ride along, comment and all")
#expect(starter.modifiedBy.isMissing, "an app-mediated write clears a foreign attribution")
#expect(try #require(starter.created.value).timeIntervalSinceNow > -60, "born today")
// The board's own blurb is its description now, untouched.
#expect(model.document.body == FixtureTemplate.blurb)
}
@Test("A symlink is copied as a link, never traversed")
func symlinksArriveAsLinks() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
let link = destination.appendingPathComponent("link.md")
let values = try link.resourceValues(forKeys: [.isSymbolicLinkKey])
#expect(values.isSymbolicLink == true)
#expect(try FileManager.default.destinationOfSymbolicLink(atPath: link.path) == "../outside.txt",
"the link itself travels, never its target")
}
@Test("A loose file beside a card's index.md lands in attachments/ — instantiation is an import boundary")
func looseCardFilesAreNormalizedOnArrival() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
let result = try BoardLoader.load(boardRoot: destination)
#expect(result.looseCardFiles.isEmpty,
"the new board lands already normalized rather than opening with a notice about its own birth")
let starter = try #require(result.model.lanes.flatMap(\.cards).first { $0.title.value == "Starter" })
#expect(starter.attachments == ["notes.txt", "shot.png"])
let card = try #require(cardFolders(under: destination).first { folder in
FileManager.default.fileExists(atPath: folder.appendingPathComponent("attachments/notes.txt").path)
})
#expect(!FileManager.default.fileExists(atPath: card.appendingPathComponent("notes.txt").path))
#expect(try Data(contentsOf: card.appendingPathComponent("attachments/notes.txt")) == Data("loose\n".utf8))
}
@Test("A legacy deleted: key copies through and is the store's to migrate, not the engine's")
func legacyTombstonesCopyThroughForTheOneMigrator() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
let result = try BoardLoader.load(boardRoot: destination)
let tombstoned = try #require(result.model.lanes.flatMap(\.cards).first { $0.title.value == "Legacy Tombstone" })
#expect(tombstoned.isDeleted, "neither stripped (a silent resurrection) nor dropped (destroyed content)")
#expect(result.legacyTombstones.count == 1,
"the new board's first load hands it to 01's one migrator, exactly as any other board's would")
}
@Test("Every identity in the tree is fresh — cards and strays under a card included")
func everyIdentityIsReminted() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "New Board")
let minted = identities(under: destination)
#expect(minted.count == 4, "two lanes and two cards — the trashed card was not copied")
#expect(minted.isDisjoint(with: identities(under: source.root)))
}
@Test("The template survives its own instantiation untouched")
func theTemplateIsNeverWritten() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let before = tree(of: source.root)
let boardBytes = try Data(contentsOf: source.root.appendingPathComponent("index.md"))
try TemplateEngine.instantiate(template: try source.template(), to: source.destination(), title: "New Board")
#expect(tree(of: source.root) == before, "the loose file was normalized in the copy, not in the template")
#expect(try Data(contentsOf: source.root.appendingPathComponent("index.md")) == boardBytes)
}
}
// MARK: - Nothing half-made
@Suite("TemplateEngine — the destination is all or nothing")
struct TemplateEngineAtomicityTests {
@Test("Cancelling mid-walk leaves nothing at the destination")
func cancellingRemovesThePartialBoard() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination()
// Trips on the fourth read: the destination exists by then and the walk is inside it, so
// there is a genuine partial tree to remove rather than nothing to clean up.
var reads = 0
let failure = instantiationFailure {
try TemplateEngine.instantiate(
template: try source.template(),
to: destination,
title: "New Board",
isCancelled: {
reads += 1
return reads > 3
}
)
}
#expect(failure == TemplateEngine.Failure.cancelled)
#expect(!FileManager.default.fileExists(atPath: destination.path),
"a cancelled create never happened")
#expect(try Set(source.fixture.entryNames("")) == [FixtureTemplate.name])
}
@Test("Cancelling before the first item never creates the destination at all")
func cancellingBeforeTheWalkCreatesNothing() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let failure = instantiationFailure {
try TemplateEngine.instantiate(
template: try source.template(),
to: source.destination(),
title: "New Board",
isCancelled: { true }
)
}
#expect(failure == TemplateEngine.Failure.cancelled)
#expect(try Set(source.fixture.entryNames("")) == [FixtureTemplate.name])
}
@Test("A destination that is already taken is refused cleanly, and never clobbered")
func collisionIsRefusedWithoutTouchingWhatIsThere() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let destination = source.destination(named: "Taken.kanban")
try FileManager.default.createDirectory(at: destination, withIntermediateDirectories: true)
try Data("mine\n".utf8).write(to: destination.appendingPathComponent("index.md"))
let failure = instantiationFailure {
try TemplateEngine.instantiate(template: try source.template(), to: destination, title: "Taken")
}
guard case let .failed(error) = failure else {
Issue.record("expected an ordinary failure, got \(String(describing: failure))")
return
}
#expect(error.operation == .createBoard)
#expect(error.path == destination.path)
#expect(try Data(contentsOf: destination.appendingPathComponent("index.md")) == Data("mine\n".utf8),
"an existing name is the user's — a create never replaces one")
#expect(try Set(FileManager.default.contentsOfDirectory(atPath: destination.path)) == ["index.md"])
}
@Test("A template that is not there fails as a create, naming the path")
func aMissingTemplateFailsCleanly() throws {
let source = try FixtureTemplate()
defer { source.tearDown() }
let template = try source.template()
try FileManager.default.removeItem(at: source.root)
let destination = source.destination()
let failure = instantiationFailure {
try TemplateEngine.instantiate(template: template, to: destination, title: "New Board")
}
guard case .failed = failure else {
Issue.record("expected an ordinary failure, got \(String(describing: failure))")
return
}
#expect(!FileManager.default.fileExists(atPath: destination.path),
"the destination this call made goes with the failure")
}
}
// MARK: - Shared
/// Every card folder under an instantiated board `<root>/<lane>/<card>`, by the loader's own level
/// detection, so the tests never hard-code a minted identity they cannot know.
private func cardFolders(under root: URL) -> [URL] {
let lanes = ((try? BoardLoader.directoryCandidates(in: root)) ?? [])
.filter { BoardLoader.isUUIDShaped($0.lastPathComponent) }
return lanes.flatMap { lane in
((try? BoardLoader.directoryCandidates(in: lane)) ?? [])
.filter { BoardLoader.isUUIDShaped($0.lastPathComponent) }
}
}