diff --git a/src/task_spec.lex b/src/task_spec.lex
index 1763540..5bde35f 100644
--- a/src/task_spec.lex
+++ b/src/task_spec.lex
@@ -263,46 +263,86 @@ fn malformed_outcome(entry :: Str) -> Outcome
   { label: label_of(Malformed(entry)), met: false, detail: "expected <path>:<kind>, e.g. src/list.lex:verified.type_check" }
 }
 
-fn target_outcome(label :: Str, target :: Str, kind :: Str) -> [io] Outcome {
-  if seen_on(verification.all(), target, kind) {
-    { label: label, met: true, detail: "" }
+# A record's `sig` binds it to the content it was a pass of (#91). A record
+# naming a specific target with no `sig`, or with a `sig` that no longer
+# matches the target's current bytes, is not evidence the current code is
+# right — it is evidence that *some* revision once was. Whole-project-scope
+# records (`target == ""`) have no single file to hash against, so they are
+# never stale by this check; that is the same limitation `sig_for` already
+# documents, not a new one.
+fn is_fresh(r :: verification.Record) -> [io] Bool {
+  if str.is_empty(r.target) {
+    true
   } else {
-    { label: label, met: false, detail: str.join(["no ", kind, " record for ", target, " in ", verification.path()], "") }
+    if str.is_empty(r.sig) {
+      false
+    } else {
+      r.sig == verification.sig_for(r.target)
+    }
   }
 }
 
-fn seen_on(records :: List[verification.Record], target :: Str, kind :: Str) -> Bool {
-  list.fold(records, false, fn (acc :: Bool, r :: verification.Record) -> Bool {
-    if acc {
-      true
-    } else {
-      if r.kind == kind {
-        r.target == target
+# Three states, not two, because "no record" and "a record, but it's stale"
+# call for different messages — a reader fixing a stale-record failure needs
+# to know a check ran before and just needs re-running, not that nothing was
+# ever checked. `Fresh` wins over `Stale` if both occur (an old stale record
+# and a newer fresh one for the same target/kind can coexist in an
+# append-only log); `Stale` wins over `Absent` otherwise.
+type Presence = Absent | Fresh | Stale
+
+fn upgrade(acc :: Presence, hit :: Bool, fresh :: Bool) -> [io] Presence {
+  match acc {
+    Fresh => Fresh,
+    _ => if hit {
+      if fresh {
+        Fresh
       } else {
-        false
+        Stale
       }
-    }
-  })
+    } else {
+      acc
+    },
+  }
 }
 
-fn verified_outcome(label :: Str, kind :: Str) -> [io] Outcome {
-  if seen(verification.all(), kind) {
-    { label: label, met: true, detail: "" }
-  } else {
-    { label: label, met: false, detail: str.join(["no ", kind, " record in ", verification.path()], "") }
-  }
+fn presence_on(records :: List[verification.Record], target :: Str, kind :: Str) -> [io] Presence {
+  list.fold(records, Absent, fn (acc :: Presence, r :: verification.Record) -> [io] Presence {
+    let hit := r.kind == kind and r.target == target
+    upgrade(acc, hit, if hit {
+      is_fresh(r)
+    } else {
+      false
+    })
+  })
 }
 
-fn seen(records :: List[verification.Record], kind :: Str) -> Bool {
-  list.fold(records, false, fn (acc :: Bool, r :: verification.Record) -> Bool {
-    if acc {
-      true
+fn presence(records :: List[verification.Record], kind :: Str) -> [io] Presence {
+  list.fold(records, Absent, fn (acc :: Presence, r :: verification.Record) -> [io] Presence {
+    let hit := r.kind == kind
+    upgrade(acc, hit, if hit {
+      is_fresh(r)
     } else {
-      r.kind == kind
-    }
+      false
+    })
   })
 }
 
+fn target_outcome(label :: Str, target :: Str, kind :: Str) -> [io] Outcome {
+  match presence_on(verification.all(), target, kind) {
+    Fresh => { label: label, met: true, detail: "" },
+    Stale => { label: label, met: false, detail: str.join(["a ", kind, " record exists for ", target, " but it no longer matches the file's current content — re-run the check"], "") },
+    Absent => { label: label, met: false, detail: str.join(["no ", kind, " record for ", target, " in ", verification.path()], "") },
+  }
+}
+
+fn verified_outcome(label :: Str, kind :: Str) -> [io] Outcome {
+  match presence(verification.all(), kind) {
+    Fresh => { label: label, met: true, detail: "" },
+    Stale => { label: label, met: false, detail: str.join(["a ", kind, " record exists in this project but no longer matches its target's current content — re-run the check"], "") },
+    Absent => { label: label, met: false, detail: str.join(["no ", kind, " record in ", verification.path()], "") },
+  }
+}
+
 # Every criterion is evaluated, not just up to the first failure. A task
 # with three unmet criteria should report three, so one round of work can
 # address all of them; short-circuiting would turn that into three rounds.
diff --git a/src/tools/linter.lex b/src/tools/linter.lex
index 70b5d8e..61e0f27 100644
--- a/src/tools/linter.lex
+++ b/src/tools/linter.lex
@@ -379,10 +379,10 @@ fn run(path :: Str) -> [io, proc] RunResult {
 # project-level file itself, not the session log dispatch_one_traced
 # writes to and session.lex later harvests from. Tool.execute's row is
 # fixed at [net, io, proc] (no `time`), so `ts_ms` is 0 rather than a
-# real clock reading; nothing that reads the file checks it for
-# freshness (task_spec.lex's `seen`/`seen_on` only check kind + target
-# exist at all), so this doesn't misrepresent anything a reader
-# actually relies on. `tool` still says "write" or "edit" rather than
+# real clock reading; `sig` (#91) is what a reader actually checks for
+# freshness, and it is real here — the file was just written and just
+# passed `lex check`, so hashing it now is hashing exactly the content
+# the pass covers. `tool` still says "write" or "edit" rather than
 # "lex_check", so the record's own provenance remains honest about
 # which of the two ways this project's file came to be verified.
 #
@@ -399,7 +399,8 @@ fn run(path :: Str) -> [io, proc] RunResult {
 fn record_verified(tool :: Str, path :: Str, result :: RunResult) -> [proc, io] Unit {
   if result.checked and not result.failed {
     let __dir := proc.run("mkdir", ["-p", ".lex"])
-    let __appended := verification.append_all([{ kind: "verified.type_check", tool: tool, target: path, ts_ms: 0 }])
+    let sig := verification.sig_for(path)
+    let __appended := verification.append_all([{ kind: "verified.type_check", tool: tool, target: path, sig: sig, ts_ms: 0 }])
     ()
   } else {
     ()
diff --git a/src/verification.lex b/src/verification.lex
index 63dab1a..a51198d 100644
--- a/src/verification.lex
+++ b/src/verification.lex
@@ -36,7 +36,18 @@ import "std.str" as str
 
 import "std.list" as list
 
-type Record = { kind :: Str, tool :: Str, target :: Str, ts_ms :: Int }
+import "std.crypto" as crypto
+
+# `sig` is a sha256 of `target`'s content at the moment the check that
+# produced this record passed. Empty means either `target` is itself empty
+# (a whole-project-scope pass has no single file to hash) or the record
+# predates this field — #91: without it, a pass recorded against one
+# revision of a file silently kept satisfying checks against a later,
+# broken revision, because nothing tied the record to the bytes it was a
+# pass *of*. `task_spec.lex`'s presence checks are what actually enforce
+# this — a record with a `sig` that no longer matches `target`'s current
+# content does not count as seen.
+type Record = { kind :: Str, tool :: Str, target :: Str, sig :: Str, ts_ms :: Int }
 
 fn path() -> Str
   examples {
@@ -75,17 +86,21 @@ fn is_verified_kind(kind :: Str) -> Bool
 
 fn encode(r :: Record) -> Str
   examples {
-    encode({ kind: "verified.type_check", tool: "lex_check", target: "src/a.lex", ts_ms: 17 }) => "{\"kind\":\"verified.type_check\",\"tool\":\"lex_check\",\"target\":\"src/a.lex\",\"ts_ms\":17}"
+    encode({ kind: "verified.type_check", tool: "lex_check", target: "src/a.lex", sig: "abc123", ts_ms: 17 }) => "{\"kind\":\"verified.type_check\",\"tool\":\"lex_check\",\"target\":\"src/a.lex\",\"sig\":\"abc123\",\"ts_ms\":17}"
   }
 {
-  jv.stringify(JObj([("kind", JStr(r.kind)), ("tool", JStr(r.tool)), ("target", JStr(r.target)), ("ts_ms", JInt(r.ts_ms))]))
+  jv.stringify(JObj([("kind", JStr(r.kind)), ("tool", JStr(r.tool)), ("target", JStr(r.target)), ("sig", JStr(r.sig)), ("ts_ms", JInt(r.ts_ms))]))
 }
 
+# A line written before `sig` existed decodes with `sig: ""` via
+# `str_field`'s missing-field default — treated as never-fresh by
+# `task_spec.lex` (a record that cannot vouch for the content it covers
+# is exactly the gap #91 closes), not as an error.
 fn decode(line :: Str) -> Option[Record] {
   match jv.parse_into_errors(str.trim(line)) {
     Err(_) => None,
     Ok(j) => match jv.get_field(j, "kind") {
-      Some(JStr(k)) => Some({ kind: k, tool: str_field(j, "tool"), target: str_field(j, "target"), ts_ms: int_field(j, "ts_ms") }),
+      Some(JStr(k)) => Some({ kind: k, tool: str_field(j, "tool"), target: str_field(j, "target"), sig: str_field(j, "sig"), ts_ms: int_field(j, "ts_ms") }),
       _ => None,
     },
   }
@@ -125,35 +140,63 @@ fn int_field(j :: jv.Json, name :: Str) -> Int {
 # tool name in `target`. They are historical and simply less precise;
 # nothing rewrites them, because a record is evidence of what was observed
 # at the time.
+#
+# `sig` is always "" here — the session log's event payload never carried
+# the target's content, only that the tool passed. `harvest` is what stamps
+# a real `sig` on afterward, by reading `target` off disk once at harvest
+# time (right after the turn, before anything else can edit it further).
 fn record_of(e :: ev.Event) -> Option[Record]
   examples {
-    record_of({ id: "x", kind: "verified.type_check", parent: None, payload_json: "{\"tool\":\"lex_check\",\"target\":\"src/a.lex\",\"result\":\"pass\"}", ts_ms: 7 }) => Some({ kind: "verified.type_check", tool: "lex_check", target: "src/a.lex", ts_ms: 7 }),
-    record_of({ id: "x", kind: "verified.test", parent: None, payload_json: "{\"tool\":\"lex_test\",\"result\":\"pass\"}", ts_ms: 8 }) => Some({ kind: "verified.test", tool: "lex_test", target: "", ts_ms: 8 }),
+    record_of({ id: "x", kind: "verified.type_check", parent: None, payload_json: "{\"tool\":\"lex_check\",\"target\":\"src/a.lex\",\"result\":\"pass\"}", ts_ms: 7 }) => Some({ kind: "verified.type_check", tool: "lex_check", target: "src/a.lex", sig: "", ts_ms: 7 }),
+    record_of({ id: "x", kind: "verified.test", parent: None, payload_json: "{\"tool\":\"lex_test\",\"result\":\"pass\"}", ts_ms: 8 }) => Some({ kind: "verified.test", tool: "lex_test", target: "", sig: "", ts_ms: 8 }),
     record_of({ id: "x", kind: "cap.completed", parent: None, payload_json: "{}", ts_ms: 9 }) => None
   }
 {
   if is_verified_kind(e.kind) {
     match jv.parse_into_errors(e.payload_json) {
       Err(_) => None,
-      Ok(j) => Some({ kind: e.kind, tool: str_field(j, "tool"), target: str_field(j, "target"), ts_ms: e.ts_ms }),
+      Ok(j) => Some({ kind: e.kind, tool: str_field(j, "tool"), target: str_field(j, "target"), sig: "", ts_ms: e.ts_ms }),
     }
   } else {
     None
   }
 }
 
+# `target`'s content hash right now, or "" when there is nothing to hash —
+# an empty target (a whole-project-scope pass) or a target this process
+# can't read. "" is also what an unhashable record decodes to, so the two
+# cases are indistinguishable on purpose: both mean "cannot vouch for this
+# as fresh," which is the conservative side to fail on.
+fn sig_for(target :: Str) -> [io] Str {
+  if str.is_empty(target) {
+    ""
+  } else {
+    match io.read(target) {
+      Err(_) => "",
+      Ok(content) => crypto.sha256_str(content),
+    }
+  }
+}
+
 # Copy this turn's verification passes out of the session log.
 #
 # `since_ms` bounds it to the turn that just ran, so a long session does not
 # re-append every earlier pass on every turn. A duplicate would not be wrong
 # — the same check really did pass twice — but it would bury the file.
-fn harvest(log :: trail_log.Log, since_ms :: Int, now_ms :: Int) -> [sql] List[Record] {
+#
+# `sig_for(r.target)` is stamped on here rather than in `record_of` because
+# only here is there anything to read: the session-log event that produced
+# `r` never carried the file's content, only that the tool passed. Reading
+# `target` now, right after the turn that produced this record, is as close
+# to "the content this pass actually covered" as the session log leaves
+# reachable.
+fn harvest(log :: trail_log.Log, since_ms :: Int, now_ms :: Int) -> [io, sql] List[Record] {
   match trail_log.range(log, since_ms, now_ms) {
     Err(_) => [],
-    Ok(events) => list.fold(events, [], fn (acc :: List[Record], e :: ev.Event) -> List[Record] {
+    Ok(events) => list.fold(events, [], fn (acc :: List[Record], e :: ev.Event) -> [io] List[Record] {
       match record_of(e) {
         None => acc,
-        Some(r) => list.concat(acc, [r]),
+        Some(r) => list.concat(acc, [{ kind: r.kind, tool: r.tool, target: r.target, sig: sig_for(r.target), ts_ms: r.ts_ms }]),
       }
     }),
   }
@@ -192,9 +235,9 @@ fn all() -> [io] List[Record] {
 # missing or unbounded.
 fn scope_of(r :: Record) -> Str
   examples {
-    scope_of({ kind: "k", tool: "lex_check", target: "src/a.lex", ts_ms: 1 }) => "src/a.lex",
-    scope_of({ kind: "k", tool: "lex_check", target: "", ts_ms: 1 }) => "the whole project",
-    scope_of({ kind: "k", tool: "", target: "lex_check", ts_ms: 1 }) => "lex_check"
+    scope_of({ kind: "k", tool: "lex_check", target: "src/a.lex", sig: "", ts_ms: 1 }) => "src/a.lex",
+    scope_of({ kind: "k", tool: "lex_check", target: "", sig: "", ts_ms: 1 }) => "the whole project",
+    scope_of({ kind: "k", tool: "", target: "lex_check", sig: "", ts_ms: 1 }) => "lex_check"
   }
 {
   if str.is_empty(r.target) {
@@ -207,8 +250,8 @@ fn scope_of(r :: Record) -> Str
 fn render(records :: List[Record]) -> Str
   examples {
     render([]) => "",
-    render([{ kind: "verified.type_check", tool: "lex_check", target: "src/a.lex", ts_ms: 17 }]) => "- verified.type_check on src/a.lex (lex_check)",
-    render([{ kind: "verified.test", tool: "", target: "", ts_ms: 1 }]) => "- verified.test on the whole project"
+    render([{ kind: "verified.type_check", tool: "lex_check", target: "src/a.lex", sig: "", ts_ms: 17 }]) => "- verified.type_check on src/a.lex (lex_check)",
+    render([{ kind: "verified.test", tool: "", target: "", sig: "", ts_ms: 1 }]) => "- verified.test on the whole project"
   }
 {
   str.join(list.map(records, fn (r :: Record) -> Str {