refactor(api): drop dead login concurrency limiter and reconcile passwordless comments

The passwordless migration (b330d77) removed the password-login route, leaving
concurrencyLimiter — its bcrypt concurrency cap — with no caller, and scattered
stale "local-password" / "change-password" references through the surviving auth
code's comments.

- Remove the dead concurrencyLimiter (type + newConcurrencyLimiter + acquire):
  no caller, no struct field, no test. Reword the one streamLimiter doc that
  contrasted against it.
- Realign comments in repo.go, pgrepo.go, session.go, util.go to the passwordless
  reality: staff lookups feed email-OTP / passkey / setup redeem, not a password
  compare; RevokeUserSessionsExcept and DeleteAllPasskeyCredentialsForUser are
  retained (uncalled) for the P5 account-remediation path (#78); "local sessions"
  no longer implies a password.

Comments and dead code only; no behavior change. Full WSL test tree green.

internal/api/api.go

@@ -622,54 +622,14 @@ func (c *cooldownLimiter) release(name string, reservedAt time.Time) {
 	}
 }
 
-// ---- login concurrency cap ----
-
-// concurrencyLimiter bounds how many holders may run a guarded section at once. It
-// backs the public login route's bcrypt cap (handleLogin): a buffered channel of n
-// tokens; acquire takes one WITHOUT blocking (returning ok=false when the section
-// is already full), release returns it. Unlike cooldownLimiter — a per-key time
-// window — this bounds simultaneity, not frequency, which is the right shape for a
-// CPU-costly section a flood would otherwise pin every core running. A non-positive
-// cap disables it (acquire always admits, release is a no-op), mirroring the "zero
-// disables" idiom of WakeCooldown and MaxRunningServers.
-type concurrencyLimiter struct {
-	slots chan struct{}
-}
-
-// newConcurrencyLimiter builds a limiter admitting at most n concurrent holders. A
-// non-positive n yields a disabled limiter (nil slots) that admits everyone.
-func newConcurrencyLimiter(n int) *concurrencyLimiter {
-	if n <= 0 {
-		return &concurrencyLimiter{}
-	}
-	return &concurrencyLimiter{slots: make(chan struct{}, n)}
-}
-
-// acquire tries to take a slot without blocking. It returns a release func and true
-// on success, or nil and false when the section is already at capacity. The disabled
-// limiter (nil slots) always admits and returns a no-op release. release MUST be
-// called exactly once on the success path, so it reads naturally as `release, ok :=
-// l.acquire(); if !ok { shed }; defer/inline release()`.
-func (l *concurrencyLimiter) acquire() (release func(), ok bool) {
-	if l.slots == nil {
-		return func() {}, true
-	}
-	select {
-	case l.slots <- struct{}{}:
-		return func() { <-l.slots }, true
-	default:
-		return nil, false
-	}
-}
-
 // ---- per-principal stream cap ----
 
 // streamLimiter bounds how many concurrent guarded sections a single KEY may hold at
 // once. It backs the per-principal SSE stream cap (console + build-log relays): each
 // relay blocks for the life of a client's attachment and, under a stalled reader,
 // pins a goroutine plus a kube-apiserver follow connection, so an unbounded number of
-// them from one principal is a control-plane connection-exhaustion vector. Unlike the
-// login concurrencyLimiter (a single global semaphore), this counts per key. A
+// them from one principal is a control-plane connection-exhaustion vector. Unlike a
+// single global semaphore, this counts per key. A
 // non-positive max disables it (acquire always admits, release is a no-op), the same
 // "zero disables" idiom as the other levers.
 type streamLimiter struct {

internal/api/pgrepo.go

@@ -722,7 +722,7 @@ func (p *PGRepo) IsProtectedAdminLink(ctx context.Context, mcUUID string) (bool,
 	return ok, err
 }
 
-// ---- local-password auth (spec §B) ----
+// ---- staff account lookups (spec §B, passwordless) ----
 
 // UserByUsername loads a staff login projection by username, or ErrNotFound.
 // The account is passwordless — staff authenticate via email-OTP / passkey, so
@@ -836,9 +836,10 @@ func (p *PGRepo) RevokeSession(ctx context.Context, tokenHash string) error {
 	return err
 }
 
-// RevokeUserSessionsExcept revokes every live session of a user except
-// keepTokenHash — the change-password flow logs out the account's other devices
-// while keeping the current one.
+// RevokeUserSessionsExcept revokes every live session of a user except keepTokenHash
+// — logs out an account's other devices while keeping the current one. Its original
+// caller (the change-password flow) was removed in the passwordless migration; it is
+// retained for the account-remediation path (P5, #78) and currently has no caller.
 func (p *PGRepo) RevokeUserSessionsExcept(ctx context.Context, userID, keepTokenHash string) error {
 	_, err := p.db.ExecContext(ctx,
 		`UPDATE sessions SET revoked_at = now()
@@ -1030,8 +1031,10 @@ func (p *PGRepo) DeletePasskeyCredential(ctx context.Context, userID, id string)
 // DeleteAllPasskeyCredentialsForUser unbinds every passkey a user holds. Unlike the
 // single-credential delete this does NOT report ErrNotFound on zero rows: removing all of
 // a user's passkeys when they have none is a successful no-op, since "the user holds no
-// passkeys" is exactly the intended post-condition. The change-password flow calls it so a
-// passkey planted through a transiently-hijacked session cannot survive the remediation.
+// passkeys" is exactly the intended post-condition. It is the remediation that stops a
+// passkey planted through a transiently-hijacked session from surviving; its original
+// caller (the change-password flow) was removed in the passwordless migration, so it is
+// currently uncalled, retained for the account-remediation/reset path (P5, #78).
 func (p *PGRepo) DeleteAllPasskeyCredentialsForUser(ctx context.Context, userID string) error {
 	_, err := p.db.ExecContext(ctx,
 		`DELETE FROM webauthn_credentials WHERE user_id = $1`, userID)

internal/api/repo.go

@@ -92,9 +92,9 @@ type StaffUser struct {
 // be public (unlike a session token), so it is safe at rest. CredentialID is the
 // authenticator's globally-unique handle (base64url) and PublicKey the COSE key
 // (base64); SignCount is the uint32 signature counter captured at registration.
-// LastUsedAt is nil until an assertion is verified — the login/step-up path that
-// would stamp it is out of scope for this enrollment-only slice (deferred), so it
-// stays nil through the flow this type backs.
+// LastUsedAt is nil until an assertion stamps it. The passkey login door now exists
+// (Public /auth/passkey/login/{begin,finish}, #72), but no path yet writes
+// last_used_at, so in practice it stays nil; wiring the stamp is a follow-up there.
 type PasskeyCredential struct {
 	ID           string
 	UserID       string
@@ -352,11 +352,13 @@ type Repo interface {
 	// can only unbind their OWN credential. No matching (user, id) row → ErrNotFound,
 	// so a stale or cross-user id cannot silently no-op as success.
 	DeletePasskeyCredential(ctx context.Context, userID, id string) error
-	// DeleteAllPasskeyCredentialsForUser unbinds every passkey a user holds. The
-	// change-password flow calls it so a passkey planted via a transiently-hijacked
-	// session does not survive the remediation (password reset + session revoke) as a
-	// standing login foothold. Removing zero rows is success, not an error — an account
-	// with no passkeys is the intended post-condition either way.
+	// DeleteAllPasskeyCredentialsForUser unbinds every passkey a user holds — the
+	// remediation that stops a passkey planted via a transiently-hijacked session from
+	// surviving as a standing login foothold. Its original caller, the change-password
+	// flow, was removed in the passwordless migration, so it currently has no production
+	// caller; it is retained for the account-remediation/reset path (P5, #78). Removing
+	// zero rows is success, not an error — an account with no passkeys is the intended
+	// post-condition either way.
 	DeleteAllPasskeyCredentialsForUser(ctx context.Context, userID string) error
 
 	// ---- player game-login: username-collision reclaim (spec §B3) ----
@@ -398,18 +400,18 @@ type Repo interface {
 	// name to protect). Keyed by UUID — the only identity velocity knows.
 	IsProtectedAdminLink(ctx context.Context, mcUUID string) (bool, error)
 
-	// ---- local-password auth (spec §B) ----
+	// ---- staff account lookups (spec §B, passwordless) ----
 
 	// UserByUsername loads the login projection of a staff account by its unique
-	// username, or ErrNotFound. The caller compares PasswordHash itself so the
-	// anti-enumeration dummy-hash compare runs even on a miss; a player row (NULL
-	// password_hash → empty PasswordHash) is returned too and is rejected by the
-	// caller's hash compare, never by leaking "no such user".
+	// username, or ErrNotFound. Its caller is the `felis breakGlass` recovery TUI,
+	// which resolves an Owner/Operator username before sending an email-OTP — there is
+	// no password compare (the account is passwordless). A non-staff (role='user') row
+	// resolves too; callers that require staff enforce the role themselves.
 	UserByUsername(ctx context.Context, username string) (*StaffUser, error)
-	// UserByID loads the same staff projection by user id, or ErrNotFound. The
-	// change-password flow uses it to re-verify the caller's current password: the
-	// session yields a user id, not a username, so this is the id-keyed counterpart
-	// of UserByUsername.
+	// UserByID loads the same staff projection by user id, or ErrNotFound. Callers hold
+	// a session (which yields a user id, not a username) and need the account behind it
+	// — e.g. setup redeem/status resolving the lockdown session's owner. It is the
+	// id-keyed counterpart of UserByUsername.
 	UserByID(ctx context.Context, id string) (*StaffUser, error)
 	// UserByEmail resolves a VERIFIED email address to its login projection,
 	// case-insensitively, or ErrNotFound (spec §B email-first login). It is the
@@ -419,9 +421,9 @@ type Repo interface {
 	// else's login by typing their email. Matching is on lower(email) to align with
 	// the users_verified_email_unique partial index (migration 0010), which
 	// guarantees at most one verified row per normalized address, so the result is
-	// unambiguous. A player row (empty PasswordHash) resolves too — email-first
-	// login is passwordless and does not consult the hash — unlike the password
-	// path, which this deliberately does not gate on.
+	// unambiguous. A player (role='user') row resolves too — email-first login is
+	// passwordless and role-agnostic here; the door that consumes this result decides
+	// what each role may do.
 	UserByEmail(ctx context.Context, email string) (*StaffUser, error)
 	// UpsertOwner creates or resets the single Owner account direct-to-Postgres
 	// (the `felis setup` / `felis breakGlass` recovery path). role is forced to

internal/api/session.go

@@ -15,23 +15,23 @@ import (
 	"time"
 )
 
-// Local-password sessions (spec §B). The remote face authenticates statelessly
-// with a Cloudflare-Access JWT and sets no cookie; local-password auth, used on
-// op.console when Zero Trust is not configured (and as the demo's primary web
-// login), needs a server-minted session. We store only the sha-256 of the opaque
-// cookie value, mirroring how service tokens are stored, so a database read never
-// yields a usable cookie.
+// Local sessions (spec §B, passwordless). The remote face authenticates statelessly
+// with a Cloudflare-Access JWT and sets no cookie; the passwordless console login
+// (email-OTP / passkey / setup redeem), used on op.console when Zero Trust is not
+// configured (and as the demo's primary web login), needs a server-minted session.
+// We store only the sha-256 of the opaque cookie value, mirroring how service tokens
+// are stored, so a database read never yields a usable cookie.
 
 const (
 	// sessionCookieName is the host-only session cookie. It carries no Domain
 	// attribute, so an op.console session is never sent to the player console.
 	sessionCookieName = "felis_session"
-	// sessionTTL bounds a local-password session. Staff re-authenticate after it.
+	// sessionTTL bounds a local session. Staff re-authenticate after it.
 	sessionTTL = 12 * time.Hour
 )
 
 // LocalAuthEnabledKey is the platform_settings key that gates whether
-// local-password sessions are honored. It is flipped on by `felis breakGlass`
+// local sessions are honored. It is flipped on by `felis breakGlass`
 // direct-to-Postgres at first-run and read live per-request, so enabling local
 // auth needs no pod roll. Exported so the break-glass writer and this
 // per-request reader share one source of truth instead of drifting copies.
@@ -109,7 +109,7 @@ func hostIsAdminConsole(r *http.Request, rootDomain, adminHostname string) bool
 }
 
 // SessionAuth is the composite ExternalAuth for the web face. It prefers a
-// local-password session cookie and otherwise delegates to the remote JWT
+// local session cookie and otherwise delegates to the remote JWT
 // verifier, so both auth models coexist on one face:
 //
 //   - No cookie  → delegate to Delegate (the Cloudflare-Access JWT path).

internal/api/util.go

@@ -12,7 +12,8 @@ const maxBodyBytes = 1 << 20 // 1 MiB
 
 // requireJSONContentType rejects a request whose body is not declared
 // application/json, returning 415 before any decode. It guards the credential-bearing
-// auth writes (login, change-password) against a cross-site forgery: an HTML form can
+// auth writes (email-OTP, passkey, op-login, setup redeem) against a cross-site
+// forgery: an HTML form can
 // only POST as application/x-www-form-urlencoded, multipart/form-data, or text/plain
 // — never JSON — and a cross-site fetch that forces application/json triggers a CORS
 // preflight this API never answers, so neither form can be forged off-origin. The