TryThis.addSuggestion mis-indents tactic sequences

Prerequisites

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• Reduce the issue to a minimal, self-contained, reproducible test case.
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• Test your test case against the latest nightly release, for example on
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Description

The TryThis suggestions API mis-indents tactic sequences. This means that (a) the info message is formatted incorrectly and (b) when clicking the code action, the tactic sequence is inserted in the wrong place, creating a syntax error. MWE:

import Lean

open Lean Lean.Meta.Tactic

elab "suggest_tac_seq" : tactic => do
  let tacSeq ← `(tacticSeq|
    skip
    skip)
  TryThis.addSuggestion (← getRef) {
    suggestion := .tsyntax tacSeq
  }

example : True := by
  suggest_tac_seq
  trivial

/-
(a) Info message:
Try this:
    skip
      skip

(b) Result of applying the code action:
example : True := by
    skip
    skip
  trivial
-/

There are also more challenging examples, but I wouldn't expect these to be formatted correctly (though this one actually remains syntactically correct).

import Lean

open Lean Lean.Meta.Tactic

elab "suggest_tac_seq" : tactic => do
  let tacSeq ← `(tacticSeq|
    skip
    skip)
  TryThis.addSuggestion (← getRef) {
    suggestion := .tsyntax tacSeq
  }

example : True := by
  first | suggest_tac_seq | fail
  trivial

/-
example : True := by
  first | 
    skip
    skip | fail
  trivial
-/

Context

aesop? uses this functionality pervasively. I previously worked around the indentation issues, but nightly breaks the workaround (Zulip).

Versions

Lean 4.24.0-nightly-2025-08-26
Target: x86_64-unknown-linux-gnu

Impact

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Reproduce the minimal examples against the cited Lean nightly, then inspect the TryThis.addSuggestion entry point and its tactic-sequence formatting and code-action insertion paths. Done means the info message uses correct indentation and applying the suggestion inserts the sequence in the correct location without introducing a syntax error.